You know what a prime number is: a number divisible only by 1 and itself. The numbers 2, 3, 5, and 7 are just a few prime numbers you probably work with everyday.

Recently, a Missouri math professor named Curtis Cooper discovered a new prime number. But it’s not likely you’ll ever use it in a math equation. The new number has 22,338,618 digits!

The ancient Greeks often get credit for first studying prime numbers. But mathematicians from all over the world have been interested in them for thousands of years. Prime numbers can help with work in cryptography, the science of writing and cracking messages written in secret codes.

During World War II, special groups in England used cryptography to learn secret information about the German military. Today, cryptography is used to protect information transferred across the Internet or on smaller computer networks.

Cooper, who teaches math at the University of Central Missouri in Warrensburg reported the new number back in September 2015. He’s part of a group of volunteers who have been searching for rare prime numbers since 1996. Known as the Great Internet Mersenne Prime Search (GIMPS), people download free computer software programmed to look for very large Mersenne prime numbers.

These special types of prime numbers are named after a French monk who lived about 350 years ago. Mersenne primes are those that result from subtracting 1 from a power of 2. The number in the exponent too is a prime number. (The number 3 is the first Mersenne prime, since 2^{2} - 1 = 3.) Only 49 Mersenne prime numbers—including one most recently discovered—are known to exist.

This isn’t the first Mersenne prime discovered at the University of Central Missouri. About 800 computers there are running the software that looks for the large numbers. “I think this number of computers has allowed us to be successful,” he says. Cooper spends one to four hours each day maintaining the machines.

According to GIMPS, the new prime number is too large to be of practical value. Though it certainly holds the record by a long shot—it’s 5 million digits longer than the previous record holder. Now that’s one for the books!