A new largest prime number has been discovered, mersenne.org reported Tuesday. 257,885,161-1, which is also the 48th Mersenne prime, was discovered on the computer of Dr. Curtis Cooper, a professor at the University of Central Missouri.

A Mersenne prime is a prime number that can be written in the form M p = 2n-1, and they’re extremely rare finds. Of all the numbers between 0 and 25,964,951 there are 1,622,441 that are prime, but only 42 are Mersenne primes.

The 48th Mersenne prime was discovered as part of the Great Internet Mersenne Prime Search (GIMPS), a project that has used volunteer computers to calculate and search for primes for 17 years. Dr. Cooper’s computer took 39 days of continuous calculation to verify the prime status of the number, which has over 17 million digits and was discovered January 25. GIMPS’ algorithm was developed in the early 1990s by Richard Crandall, an Apple Distinguished Scientist.

Mersenne.org states that the discovery was verified independently by a few different computers: a 32-core server took 6 days running MLucas software to confirm; CUDALucas software running on an Nvidia GTX 560 Ti took 7.7 days; and the GIMPS software on an Intel Core i7 CPU took 4.5 days. If the 17 million digits were written out, they would fill approximately 28 novel-length books.

Thus far, 14 Mersenne primes have been discovered under GIMPS, including the 48th, with the last discovery occurring in April 2009. Per the rules of GIMPS, Dr. Cooper will receive a grant of $3,000 for his help. Interested participants can download the free program to help in the prime number hunt.