For those not in the math know, a prime number is a special kind of number that can only be divided by itself and one. The search party, called the Great Internet Mersenne Prime Search, is actually searching for an even more unique number — a special kind of prime number called a Mersenne prime, a prime number that can be written in scientific shorthand 2p - 1, where the exponent is itself a prime. In this example, 57,885,161 is the prime exponent.

 

This new number is only the 48th Mersenne prime ever found. It's also the biggest. The second largest Mersenne prime has just under 13 million digits. Here's how they do it, explained by Jacob Aron of New Scientist:

 

Though there are an infinite number of primes, there is no formula for generating these numbers, so discovering them requires intensive computation. GIMPS uses volunteers' computers to sift through each prime-number candidate in turn, until eventually one lucky user discovers a new prime.