NewPGen is a program used by researchers looking for large prime numbers. It is a program that is used to rapidly presieve a set of candidate numbers, removing those that are definitely composite numbers. It does this by removing those numbers divisible by 3, 5, etc, but since it works with a large set of numbers (and uses some clever algorithms and fast implementations), it is a lot better than performing trial division on each number in the set. Those numbers which get through this sieve would then be tested with a primality proving program to find the primes.

NewPGen has been used to make many discoveries in the realm of prime numbers, for example the largest known twin prime

Twin prime

A twin prime is a prime number that differs from another prime number by two. Except for the pair , this is the smallest possible difference between two primes. Some examples of twin prime pairs are , , , , and...

s, and nearly all of the known cunningham chain

Cunningham chain

In mathematics, a Cunningham chain is a certain sequence of prime numbers. Cunningham chains are named after mathematician A. J. C. Cunningham. They are also called chains of nearly doubled primes....

s. It is written and maintained by Paul Jobling.