28 (number)
Encyclopedia
28 is the natural number
Natural number
In mathematics, the natural numbers are the ordinary whole numbers used for counting and ordering . These purposes are related to the linguistic notions of cardinal and ordinal numbers, respectively...

 following 27
27 (number)
27 is the natural number following 26 and preceding 28.- In mathematics :Twenty-seven is a perfect cube, being 33 = 3 × 3 × 3. 27 is also 23 . There are exactly 27 straight lines on a smooth cubic surface, which give a basis of the fundamental representation of the E6 Lie algebra...

 and preceding 29
29 (number)
29 is the natural number following 28 and preceding 30.-In mathematics:It is the tenth prime number, and also the fourth primorial prime. It forms a twin prime pair with thirty-one, which is also a primorial prime. Twenty-nine is also the sixth Sophie Germain prime. It is also the sum of three...

.

In mathematics

It is a composite number
Composite number
A composite number is a positive integer which has a positive divisor other than one or itself. In other words a composite number is any positive integer greater than one that is not a prime number....

, its proper divisor
Divisor
In mathematics, a divisor of an integer n, also called a factor of n, is an integer which divides n without leaving a remainder.-Explanation:...

s being 1, 2, 4, 7, and 14
14 (number)
14 is the natural number following 13 and preceding 15.In speech, the numbers 14 and 40 are often confused. When carefully enunciated, they differ in which syllable is stressed: 14 vs 40...

.

Twenty-eight is the second perfect number
Perfect number
In number theory, a perfect number is a positive integer that is equal to the sum of its proper positive divisors, that is, the sum of its positive divisors excluding the number itself . Equivalently, a perfect number is a number that is half the sum of all of its positive divisors i.e...

. As a perfect number, it is related to the Mersenne prime
Mersenne prime
In mathematics, a Mersenne number, named after Marin Mersenne , is a positive integer that is one less than a power of two: M_p=2^p-1.\,...

 7, since 22(23 - 1) = 28. The next perfect number is 496
496 (number)
Four hundred [and] ninety-six is the natural number following four hundred [and] ninety-five and preceding four hundred [and] ninety-seven.-In mathematics:...

, the previous being 6.

Twenty-eight is the third Granville number. The next Granville number is 96
96 (number)
96 is the natural number following 95 and preceding 97.-In mathematics:Ninety-six is an octagonal number, a refactorable number and an untouchable number. Since it is a multiple of 6, it is a semiperfect number...

, the previous being 24
24 (number)
24 is the natural number following 23 and preceding 25.The SI prefix for 1024 is yotta , and for 10−24 yocto...

.

Twenty-eight is the sum of the totient function for the first nine integers.

Twenty-eight is not the aliquot sum of any number other than itself and is therefore not a component in an aliquot sequence
Aliquot sequence
In mathematics, an aliquot sequence is a recursive sequence in which each term is the sum of the proper divisors of the previous term. The aliquot sequence starting with a positive integer k can be defined formally in terms of the sum-of-divisors function σ1 in the following way:For example, the...

.

Since the greatest prime factor
Prime factor
In number theory, the prime factors of a positive integer are the prime numbers that divide that integer exactly, without leaving a remainder. The process of finding these numbers is called integer factorization, or prime factorization. A prime factor can be visualized by understanding Euclid's...

 of 282 + 1 = 785 is 157, which is more than 28 twice, 28 is a Størmer number
Størmer number
In mathematics, a Størmer number or arc-cotangent irreducible number, named after Carl Størmer, is a positive integer n for which the greatest prime factor of n2 + 1 meets or exceeds 2n. The first few Størmer numbers are 1, 2, 4, 5, 6, 9, 10, 11, 12, 14, 15, 16, 19, 20, etc....

.

Twenty-eight is a harmonic divisor number
Harmonic divisor number
In mathematics, a harmonic divisor number, or Ore number , is a positive integer whose divisors have a harmonic mean that is an integer. The first few harmonic divisor numbers are...

, a happy number
Happy number
A happy number is defined by the following process. Starting with any positive integer, replace the number by the sum of the squares of its digits, and repeat the process until the number equals 1 , or it loops endlessly in a cycle which does not include 1...

, a triangular number
Triangular number
A triangular number or triangle number numbers the objects that can form an equilateral triangle, as in the diagram on the right. The nth triangle number is the number of dots in a triangle with n dots on a side; it is the sum of the n natural numbers from 1 to n...

, a hexagonal number
Hexagonal number
A hexagonal number is a figurate number. The nth hexagonal number will be the number of points in a hexagon with n regularly spaced points on a side.The formula for the nth hexagonal number...

, and a centered nonagonal number
Centered nonagonal number
A centered nonagonal number is a centered figurate number that represents a nonagon with a dot in the center and all other dots surrounding the center dot in successive nonagonal layers...

.

It appears in the Padovan sequence
Padovan sequence
The Padovan sequence is the sequence of integers P defined by the initial valuesP=P=P=1,and the recurrence relationP=P+P.The first few values of P are...

, preceded by the terms 12, 16, 21 (it is the sum of the first two of these).

It is also a Keith number, because it recurs in a Fibonacci-like sequence started from its base 10 digits: 2, 8, 10, 18, 28...

Twenty-eight is the third positive integer with a prime factorization of the form where q is an odd prime.

Twenty-eight is the ninth and last number in early India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...

n magic square
Magic square
In recreational mathematics, a magic square of order n is an arrangement of n2 numbers, usually distinct integers, in a square, such that the n numbers in all rows, all columns, and both diagonals sum to the same constant. A normal magic square contains the integers from 1 to n2...

 of order 3.

There are twenty-eight convex uniform honeycomb
Convex uniform honeycomb
In geometry, a convex uniform honeycomb is a uniform tessellation which fills three-dimensional Euclidean space with non-overlapping convex uniform polyhedral cells.Twenty-eight such honeycombs exist:* the familiar cubic honeycomb and 7 truncations thereof;...

s.

Twenty-eight is the only positive integer that has a unique Kayles
Kayles
In combinatorial game theory, Kayles is a simple impartial game. In the notation of octal games, Kayles is denoted 0.77.- Rules :Kayles is played with a row of tokens, which represent bowling pins. The row may be of any length...

 nim-value.

In science

  • The atomic mass
    Atomic mass
    The atomic mass is the mass of a specific isotope, most often expressed in unified atomic mass units. The atomic mass is the total mass of protons, neutrons and electrons in a single atom....

     of silicon
    Silicon
    Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...

    .
  • The atomic number
    Atomic number
    In chemistry and physics, the atomic number is the number of protons found in the nucleus of an atom and therefore identical to the charge number of the nucleus. It is conventionally represented by the symbol Z. The atomic number uniquely identifies a chemical element...

     of nickel
    Nickel
    Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile...

    .
  • The fourth magic number
    Magic number (physics)
    In nuclear physics, a magic number is a number of nucleons such that they are arranged into complete shells within the atomic nucleus...

     in physics.
  • The curing time of concrete
    Concrete
    Concrete is a composite construction material, composed of cement and other cementitious materials such as fly ash and slag cement, aggregate , water and chemical admixtures.The word concrete comes from the Latin word...

     is classically considered 28 days.
  • The average human menstrual cycle
    Menstrual cycle
    The menstrual cycle is the scientific term for the physiological changes that can occur in fertile women for the purpose of sexual reproduction. This article focuses on the human menstrual cycle....

     is 28 days although no link has been established with the nightlighting and the Moon.

Astronomy

  • The revolution time of the surface of the Sun
    Sun
    The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...

     on itself is 28 days while its core is revolving in 33 days.

  • Messier object
    Messier object
    The Messier objects are a set of astronomical objects first listed by French astronomer Charles Messier in 1771. The original motivation of the catalogue was that Messier was a comet hunter, and was frustrated by objects which resembled but were not comets...

     M28
    Messier 28
    Messier 28 is a globular cluster in the constellation Sagittarius. It was discovered by Charles Messier in 1764. In the sky it is very close to the 3rd magnitude star Kaus Borealis....

    , a magnitude 8.5 globular cluster
    Globular cluster
    A globular cluster is a spherical collection of stars that orbits a galactic core as a satellite. Globular clusters are very tightly bound by gravity, which gives them their spherical shapes and relatively high stellar densities toward their centers. The name of this category of star cluster is...

     in the constellation
    Constellation
    In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....

     Sagittarius
    Sagittarius (constellation)
    Sagittarius is a constellation of the zodiac, the one containing the galactic center. Its name is Latin for the archer, and its symbol is , a stylized arrow. Sagittarius is commonly represented as a centaur drawing a bow...

    .

  • The New General Catalogue
    New General Catalogue
    The New General Catalogue of Nebulae and Clusters of Stars is a well-known catalogue of deep sky objects in astronomy. It contains 7,840 objects, known as the NGC objects...

     object NGC 28
    NGC 28
    NGC 28 is an elliptical galaxy located in the Phoenix constellation....

    , an elliptical galaxy
    Elliptical galaxy
    An elliptical galaxy is a galaxy having an approximately ellipsoidal shape and a smooth, nearly featureless brightness profile. They range in shape from nearly spherical to highly flat and in size from hundreds of millions to over one trillion stars...

     in the constellation Phoenix
    Phoenix (constellation)
    Phoenix is a minor constellation in the southern sky. It is named after the Phoenix, a mythical bird. It is faint: there are only two stars in the whole constellation which are brighter than magnitude 5.0...

    .

  • The Saros number of the solar eclipse
    Solar eclipse
    As seen from the Earth, a solar eclipse occurs when the Moon passes between the Sun and the Earth, and the Moon fully or partially blocks the Sun as viewed from a location on Earth. This can happen only during a new moon, when the Sun and the Moon are in conjunction as seen from Earth. At least...

     series which began on -1910 March 22 and ended on -630 April 28. The duration of Saros series 28 was 1280.1 years, and it contained 72 solar eclipses.

  • The Saros number of the lunar eclipse
    Lunar eclipse
    A lunar eclipse occurs when the Moon passes behind the Earth so that the Earth blocks the Sun's rays from striking the Moon. This can occur only when the Sun, Earth, and Moon are aligned exactly, or very closely so, with the Earth in the middle. Hence, a lunar eclipse can only occur the night of a...

     series which began on -1915 June 27 and ended on -581 September 6. The duration of Saros series 28 was 1334.2 years, and it contained 75 lunar eclipses.


In sports

  • The jersey number 28 has been retired by several North American sports teams in honor of past playing greats or other key figures:
    • In Major League Baseball
      Major League Baseball
      Major League Baseball is the highest level of professional baseball in the United States and Canada, consisting of teams that play in the National League and the American League...

      :
      • The Minnesota Twins
        Minnesota Twins
        The Minnesota Twins are a professional baseball team based in Minneapolis, Minnesota. They play in the Central Division of Major League Baseball's American League. The team is named after the Twin Cities area of Minneapolis and St. Paul. They played in Metropolitan Stadium from 1961 to 1981 and the...

        , for Hall of Famer
        National Baseball Hall of Fame and Museum
        The National Baseball Hall of Fame and Museum is an American history museum and hall of fame, located at 25 Main Street in Cooperstown, New York, operated by private interests serving as the central point for the study of the history of baseball in the United States and beyond, the display of...

         Bert Greenburg
    • In the NFL
      National Football League
      The National Football League is the highest level of professional American football in the United States, and is considered the top professional American football league in the world. It was formed by eleven teams in 1920 as the American Professional Football Association, with the league changing...

      :
      • The Chicago Bears
        Chicago Bears
        The Chicago Bears are a professional American football team based in Chicago, Illinois. They are members of the North Division of the National Football Conference in the National Football League...

        , for Willie Galimore
        Willie Galimore
        Willie Galimore was an American football running back for the Chicago Bears from 1957-1963. He attended Florida A&M University, working with the legendary coach Jake Gaither...

        .
      • The Kansas City Chiefs
        Kansas City Chiefs
        The Kansas City Chiefs are a professional American football team based in Kansas City, Missouri. They are a member of the Western Division of the American Football Conference in the National Football League . Originally named the Dallas Texans, the club was founded by Lamar Hunt in 1960 as a...

        , for Abner Haynes
        Abner Haynes
        Abner Haynes is a former college and professional football player in the United States.Haynes is a graduate of North Texas State University where he and his then teammate Leon King integrated college football in the state of Texas in 1956...

        .
      • The New York Jets
        New York Jets
        The New York Jets are a professional football team headquartered in Florham Park, New Jersey, representing the New York metropolitan area. The team is a member of the Eastern Division of the American Football Conference in the National Football League...

        , for Curtis Martin
        Curtis Martin
        Curtis James Martin, Jr. is a former American football running back. He is an alumnus of Taylor Allderdice High School in Pittsburgh and the University of Pittsburgh...

        .
      • The St. Louis Rams
        St. Louis Rams
        The St. Louis Rams are a professional American football team based in St. Louis, Missouri. They are currently members of the West Division of the National Football Conference in the National Football League . The Rams have won three NFL Championships .The Rams began playing in 1936 in Cleveland,...

        , for Hall of Famer
        Pro Football Hall of Fame
        The Pro Football Hall of Fame is the hall of fame of professional football in the United States with an emphasis on the National Football League . It opened in Canton, Ohio, on September 7, 1963, with 17 charter inductees...

         Marshall Faulk
        Marshall Faulk
        Marshall William Faulk is a former American football running back who played in the National Football League. He is currently an analyst for NFL Total Access, Thursday Night Football, and NFL GameDay Morning on the NFL Network...

        .
  • The NBA
    National Basketball Association
    The National Basketball Association is the pre-eminent men's professional basketball league in North America. It consists of thirty franchised member clubs, of which twenty-nine are located in the United States and one in Canada...

     and NHL
    National Hockey League
    The National Hockey League is an unincorporated not-for-profit association which operates a major professional ice hockey league of 30 franchised member clubs, of which 7 are currently located in Canada and 23 in the United States...

     both operate four best-of-seven rounds during the playoffs; thus, 28 is the maximum number of games that a team could possibly play in the playoff series (neither league has ever had a team play that many games, though).
  • The number worn by the Clemson Tigers' record breaking running back C.J. Spiller, former Colts and Rams running back Marshall Faulk, former Bucs and Falcons running back Warrick Dunn, former Kansas City Chiefs running back Abner Haynes
    Abner Haynes
    Abner Haynes is a former college and professional football player in the United States.Haynes is a graduate of North Texas State University where he and his then teammate Leon King integrated college football in the state of Texas in 1956...

    , current Titans running back Chris Johnson.
  • The number used by former NASCAR
    NASCAR
    The National Association for Stock Car Auto Racing is a family-owned and -operated business venture that sanctions and governs multiple auto racing sports events. It was founded by Bill France Sr. in 1947–48. As of 2009, the CEO for the company is Brian France, grandson of the late Bill France Sr...

     driver Davey Allison
    Davey Allison
    David Carl "Davey" Allison was a NASCAR driver. He was best known for driving the #28 Texaco-Havoline Ford for Robert Yates Racing in the Winston Cup Series. Born in Hollywood, Florida, he was the eldest of four children born to Bobby Allison and wife Judy...

     for his entire NASCAR Winston Cup career.

In other fields

Twenty-eight is:
  • An abbreviation for such years as 1928 and 2028.
  • In Gematriya, the system of Hebrew Numerology
    Numerology
    Numerology is any study of the purported mystical relationship between a count or measurement and life. It has many systems and traditions and beliefs...

    , the number 28 corresponds to the word koakh, meaning "power", "energy".
  • The number of days in the shortest month
    Month
    A month is a unit of time, used with calendars, which was first used and invented in Mesopotamia, as a natural period related to the motion of the Moon; month and Moon are cognates. The traditional concept arose with the cycle of moon phases; such months are synodic months and last approximately...

     of the Gregorian calendar
    Gregorian calendar
    The Gregorian calendar, also known as the Western calendar, or Christian calendar, is the internationally accepted civil calendar. It was introduced by Pope Gregory XIII, after whom the calendar was named, by a decree signed on 24 February 1582, a papal bull known by its opening words Inter...

    , February
    February
    February is the second month of the year in the Julian and Gregorian calendars. It is the shortest month and the only month with fewer than 30 days. The month has 28 days in common years and 29 days in leap years...

     (except in leap year
    Leap year
    A leap year is a year containing one extra day in order to keep the calendar year synchronized with the astronomical or seasonal year...

    s, when there are twenty-nine). All twelve months of the Gregorian calendar have at least 28 days, regardless of the year.
  • The Gregorian calendar
    Gregorian calendar
    The Gregorian calendar, also known as the Western calendar, or Christian calendar, is the internationally accepted civil calendar. It was introduced by Pope Gregory XIII, after whom the calendar was named, by a decree signed on 24 February 1582, a papal bull known by its opening words Inter...

     follows a 28-year cycle for the most part, since there are seven days in a week and leap year generally occurs every four years; usually, a calendar from any year is the same as that from 28 years earlier (e.g., 2008 and 1980). However, that rule holds only when there have been exactly seven leap days in a 28-year interval; years divisible by 100 but not by 400 are not leap years. Indeed, 1900 (as well as 2100, 2200, etc.) does not use the same calendar as 1872 (2072, 2172, etc., respectively) for the simple reason that 1900 is not a leap year. In 28 years, any day-of-the-week and date combination occurs exactly four times. February 29 will fall on each day of the week once.
  • The common name for the parrot
    Parrot
    Parrots, also known as psittacines , are birds of the roughly 372 species in 86 genera that make up the order Psittaciformes, found in most tropical and subtropical regions. The order is subdivided into three families: the Psittacidae , the Cacatuidae and the Strigopidae...

     'Barnardius zonarius semitorquatus'
    Australian Ringneck
    The Australian Ringneck is a parrot native to Australia. Except for extreme tropical and highland areas, the species has adapted to all conditions...

    , widely distributed in Western Australia
    Western Australia
    Western Australia is a state of Australia, occupying the entire western third of the Australian continent. It is bounded by the Indian Ocean to the north and west, the Great Australian Bight and Indian Ocean to the south, the Northern Territory to the north-east and South Australia to the south-east...

     and South Australia
    South Australia
    South Australia is a state of Australia in the southern central part of the country. It covers some of the most arid parts of the continent; with a total land area of , it is the fourth largest of Australia's six states and two territories.South Australia shares borders with all of the mainland...

    . Its call sounds like "wenniate".
  • The number of letters in the Danish and Swedish
    Swedish alphabet
    Modern Swedish is written with a 29-letter Latin alphabet:Prior to the 13th edition of Svenska Akademiens ordlista in 2006, the letters and were collated together....

     alphabet
    Alphabet
    An alphabet is a standard set of letters—basic written symbols or graphemes—each of which represents a phoneme in a spoken language, either as it exists now or as it was in the past. There are other systems, such as logographies, in which each character represents a word, morpheme, or semantic...

    s (not counting W), and also in the Arabic
    Arabic alphabet
    The Arabic alphabet or Arabic abjad is the Arabic script as it is codified for writing the Arabic language. It is written from right to left, in a cursive style, and includes 28 letters. Because letters usually stand for consonants, it is classified as an abjad.-Consonants:The Arabic alphabet has...

     and Esperanto
    Esperanto orthography
    Esperanto is written in a Latin alphabet of twenty-eight letters, with upper and lower case. This is supplemented by punctuation marks and by various logograms, such as the numerals 0–9, currency signs such as $, and mathematical symbols....

     alphabet
    Alphabet
    An alphabet is a standard set of letters—basic written symbols or graphemes—each of which represents a phoneme in a spoken language, either as it exists now or as it was in the past. There are other systems, such as logographies, in which each character represents a word, morpheme, or semantic...

    s.
  • In neo-Nazi circles, twenty-eight indicates Blood and Honour
    Blood and Honour
    Blood & Honour is a neo-Nazi music promotion network and political group founded in 1987 with links to Combat 18 and composed of white power skinheads and other white nationalists....

     (28 = BH - B - second letter of the alphabet and H - the eight letter).
  • The number of Chinese constellation
    Constellation
    In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....

    s, "Xiu" or "mansions" (a literal translation), equivalent to the 12 western zodiac
    Zodiac
    In astronomy, the zodiac is a circle of twelve 30° divisions of celestial longitude which are centred upon the ecliptic: the apparent path of the Sun across the celestial sphere over the course of the year...

     constellations.
  • The number of dominoes
    Dominoes
    Dominoes generally refers to the collective gaming pieces making up a domino set or to the subcategory of tile games played with domino pieces. In the area of mathematical tilings and polyominoes, the word domino often refers to any rectangle formed from joining two congruent squares edge to edge...

     in standard domino sets.
  • Deriving from the 29.46 year period of Saturn
    Saturn
    Saturn is the sixth planet from the Sun and the second largest planet in the Solar System, after Jupiter. Saturn is named after the Roman god Saturn, equated to the Greek Cronus , the Babylonian Ninurta and the Hindu Shani. Saturn's astronomical symbol represents the Roman god's sickle.Saturn,...

    's revolution around the Sun
    Sun
    The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...

    , the 28-year cycle as well as its subdivisions by 14 and 7 are supposed in Astrology
    Astrology
    Astrology consists of a number of belief systems which hold that there is a relationship between astronomical phenomena and events in the human world...

     to mark significant turning points or sections in the course of a persons development in life. Thus, the number 28 has special significance in the culture of religious sects such as the Kadiri
    Kadiri
    Kadiri is a Small town, Mandal and a municipality in the southeastern part of Anantapur district in Andhra Pradesh, India. The Lord Lakshmi Narasimha Swamy Temple is located in this town, and large numbers of Hindu pilgrims visit the Temple throughout the year. The Thimmamma Marrimanu Kadiri is...

     and the Mevlevi
    Mevlevi
    The Mevlevi Order, or the Mevlevilik or Mevleviye are a Sufi order founded in Konya by the followers of Jalal ad-Din Muhammad Balkhi-Rumi, a 13th century Persian poet, Islamic jurist, and theologian. They are also known as the Whirling Dervishes due to their famous practice of whirling as a form...

     dervishes. The 28-beat metric pattern often used in the music compositions accompanying the main part of the Mevlevi
    Mevlevi
    The Mevlevi Order, or the Mevlevilik or Mevleviye are a Sufi order founded in Konya by the followers of Jalal ad-Din Muhammad Balkhi-Rumi, a 13th century Persian poet, Islamic jurist, and theologian. They are also known as the Whirling Dervishes due to their famous practice of whirling as a form...

     sema
    Sema
    Sama is a Sufi ceremony performed as dhikr. Sama means "listening", while dhikr means "remembrance". These rituals often includes singing, playing instruments, dancing, recitation of poetry and prayers, wearing symbolic attire, and other rituals...

     ritual is called the "Devri kebir", meaning the "Big Circle" and is a reference to above astronomical facts about the year and the Saturn year.
  • In Quebec
    Quebec
    Quebec or is a province in east-central Canada. It is the only Canadian province with a predominantly French-speaking population and the only one whose sole official language is French at the provincial level....

    , François Pérusse
    François Pérusse
    François Pérusse is a Québécois comedian and musician famous for his radio sketches featuring puns and absurd humor. His best-known sketches are from the series Les 2 minutes du peuple...

    , in one of his best-selling Album du peuple made a parody of Wheel of Fortune
    Wheel of Fortune (U.S. game show)
    Wheel of Fortune is an American television game show created by Merv Griffin, which premiered in 1975. Contestants compete to solve word puzzles, similar to those used in Hangman, to win cash and prizes determined by spinning a large wheel. The title refers to the show's giant carnival wheel that...

     in which all of the letters picked by the contestant were present 28 times. As a result, 28 became an almost Mythical number
    Mythical number
    Not to be confused with an imaginary number.A mythical number is a number used and accepted as deriving from scientific investigation and/or careful selection, but whose origin is unknown and whose basis is unsubstantiated. An example is the number 48 billion, which has often been accepted as the...

     used by many Quebec youths, the phrase "Y'en a 28" (There are 28 [Letters]) became a running gag
    Running gag
    A running gag, or running joke, is a literary device that takes the form of an amusing joke or a comical reference and appears repeatedly throughout a work of literature or other form of storytelling....

     still used and recognized more than 15 years later.
  • The Preludes, Opus 28
    Preludes Op. 28 (Chopin)
    Frédéric Chopin wrote a number of preludes for piano solo.-24 Preludes, Op. 28:Chopin's 24 Preludes, Op. 28, are a set of short pieces for the piano, one in each of the twenty-four keys, originally published in 1839 and dedicated to Joseph Christoph Kessler, a composer of piano studies during...

     consists of Frédéric Chopin
    Frédéric Chopin
    Frédéric François Chopin was a Polish composer and virtuoso pianist. He is considered one of the great masters of Romantic music and has been called "the poet of the piano"....

    's 24 preludes for piano, ordinarily but not necessarily played together in concert.
  • The postal code
    Postal code
    A postal code is a series of letters and/or digits appended to a postal address for the purpose of sorting mail. Once postal codes were introduced, other applications became possible.In February 2005, 117 of the 190 member countries of the Universal Postal Union had postal code systems...

     of the province of Madrid, in Spain
    Spain
    Spain , officially the Kingdom of Spain languages]] under the European Charter for Regional or Minority Languages. In each of these, Spain's official name is as follows:;;;;;;), is a country and member state of the European Union located in southwestern Europe on the Iberian Peninsula...

    .
  • Twenty Eight
    Twenty-eight (card game)
    This is one of a group of Indian trick-taking card games in which the Jack and the Nine are the highest cards in every suit.-Players and cards:28 is usually played by four players in fixed partnerships, partners facing each other. 32 cards from a standard 52-card pack are used for play. There are...

     is a popular game played in Kerala India.
  • The number of the French department Eure-et-Loir
    Eure-et-Loir
    Eure-et-Loir is a French department, named after the Eure and Loir rivers.-History:Eure-et-Loir is one of the original 83 departments created during the French Revolution on March 4, 1790 pursuant to the Act of December 22, 1789...

    .
  • Approximately the number of grams in an ounce, and used as such in the illegal drug trade.
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