Knuth reward checks are awarded by computer scientist Donald Knuth

Donald Knuth

Donald Ervin Knuth is a computer scientist and Professor Emeritus at Stanford University.He is the author of the seminal multi-volume work The Art of Computer Programming. Knuth has been called the "father" of the analysis of algorithms...

 for finding mistakes in, or making suggestions for, his publications. In the preface of each of his books and on his website, Knuth offers a reward of $2.56 (USD) to the first person to find each error in his published books, whether it be technical, typographical, or historical. Knuth explains that $2.56, or 256 cents, corresponds to one hexadecimal

Hexadecimal

In mathematics and computer science, hexadecimal is a positional numeral system with a radix, or base, of 16. It uses sixteen distinct symbols, most often the symbols 0–9 to represent values zero to nine, and A, B, C, D, E, F to represent values ten to fifteen...

 dollar. Valuable suggestions are worth 32¢. (In his earlier books a smaller reward was offered. For example, the 2nd edition of The Art of Computer Programming, Volume 1, offered $2.00.)

Initially, Knuth sent real checks to recipients. He stopped doing so in October 2008 because of problems with check fraud. As a replacement, he started his own "Bank of San Serriffe," in the fictional nation of San Serriffe

San Serriffe

San Serriffe is a fictional island nation created for April Fools' Day, 1977, by Britain's Guardian newspaper. An elaborate description of the nation, using puns and plays on words relating to typography , was reported as legitimate news, apparently fooling many readers...

, which keeps an account for everyone who found an error since 2006. Knuth also sends out "hexadecimal certificates" instead of checks.

According to an article in the Massachusetts Institute of Technology

Massachusetts Institute of Technology

The Massachusetts Institute of Technology is a private research university located in Cambridge, Massachusetts. MIT has five schools and one college, containing a total of 32 academic departments, with a strong emphasis on scientific and technological education and research.Founded in 1861 in...

's Technology Review

Technology Review

Technology Review is a magazine published by the Massachusetts Institute of Technology. It was founded in 1899 as "The Technology Review", and was re-launched without the "The" in its name on April 23, 1998 under then publisher R. Bruce Journey...

, these rewards have been described as "among computerdom's most prized trophies". , Knuth reports having written more than 2,000 checks, with an average value exceeding $8 per check. , the total value of the checks signed by Knuth was over $20,000 (see NPR interview below). Very few of these checks are actually cashed, however, even the largest ones; more often, they are framed, or kept as "bragging rights".
The reward for coding errors found in Knuth's TeX

TeX

TeX is a typesetting system designed and mostly written by Donald Knuth and released in 1978. Within the typesetting system, its name is formatted as ....

 and METAFONT

METAFONT

Metafont is a programming language used to define vector fonts. It is also the name of the interpreter that executes Metafont code, generating the bitmap fonts that can be embedded into e.g. PostScript...

 programs (as distinguished from errors in Knuth's books) followed an audacious scheme inspired by the Wheat and Chessboard Problem

Wheat and Chessboard Problem

The wheat and chessboard problem is a mathematical problem: To solve this, observe that a chess board is an 8×8 square, containing 64 squares...

. It started at $1.28, and doubled every year until it reached $327.68. Recipients of this "sweepstakes" reward include Chris Thompson (Cambridge) and Boguslaw Jackowski (Gdansk), and also Peter Breitenlohner on 20 March 1995.

Knuth is often unable to answer immediately when a reader finds a mistake in one of his books or programs; in some cases, the delay has been several years long. For example, on 1 July 1996, Knuth sent out more than 250 letters, 125 of which contained checks, for errors reported in The Art of Computer Programming

The Art of Computer Programming

The Art of Computer Programming is a comprehensive monograph written by Donald Knuth that covers many kinds of programming algorithms and their analysis....

since the summer of 1981. A few of these remain unclaimed as of May 2006. When Knuth is not able to reply immediately, he adds 5% interest, compounded continuously, to the reward.

Each check's memo field identifies the book and page number. 1.23 indicates an error on page 23 of Volume 1. (1.23) indicates a valuable suggestion on that page. The symbol Θ (a Greek theta

Theta

Theta is the eighth letter of the Greek alphabet, derived from the Phoenician letter Teth...

, making a 'th' sound) denotes the book Things a Computer Scientist Rarely Talks About

Things a Computer Scientist Rarely Talks About

Things a Computer Scientist Rarely Talks About is a book by Donald E. Knuth, published by CLSI Publications of Stanford, California. The book contains the annotated transcripts of six public lectures given by Donald E. Knuth at MIT on the subject of relations between religion and science...

, KLR denotes the book Mathematical Writing (by Knuth, Larrabee, and Roberts), GKP and CM denote the book Concrete Mathematics

Concrete Mathematics

Concrete Mathematics: A Foundation for Computer Science, by Ronald Graham, Donald Knuth, and Oren Patashnik, is a mathematical textbook that is widely used in computer-science departments. It provides mathematical knowledge and skills for computer science, especially for the analysis of algorithms...

(by Graham, Knuth, and Patashnik), f1 denotes fascicle 1, CMT denotes the book Computer Modern Typefaces, DT denotes the book Digital Typography, SN denotes Surreal Numbers, CWEB denotes the book The CWEB System of Structured Documentation, DA denotes the book Selected Papers on Design of Algorithms, and FG denotes the book Selected Papers on Fun and Games.

External links

• The Bank of San Serriffe
• Interview (RealVideo
  RealVideo
  RealVideo is a suite of proprietary video compression formats developed by RealNetworks – the specific format changes with the version. It was first released in 1997 and is at version 10. RealVideo is supported on many platforms, including Windows, Mac, Linux, Solaris, and several mobile...
  
   format) (or Transcript) with Knuth on National Public Radio