# The largest known prime number has 23 million-plus digits

An electrical engineer from Tennessee made the discovery

There’s a new largest known prime number in town, with a whopping 23,249,425 digits. The figure is calculated by multiplying 2 by itself 77,232,917 times and then subtracting 1. Announced on January 3, the number is almost a million digits longer than the last record-breaking prime.

A prime number can’t be divided by anything other than 1 and itself. If you started counting at 1, you’d encounter prime numbers relatively frequently at first. But as numbers get larger, primes become sparse.

Jonathan Pace, an electrical engineer in Germantown, Tenn., found the number using software provided by the Great Internet Mersenne Prime Search. GIMPS is a volunteer-based project that’s seeking ever-higher Mersenne primes, which are found by multiplying the number 2 by itself some number of times and subtracting 1. These primes are easier to find than other types, Pace says, because the computer doesn’t need to calculate a number’s divisors to determine whether or not it’s prime.

Pace started hunting for primes 14 years ago, when there was a cash reward for finding a prime number with more than 10 million digits. “I missed out on the big prize,” he says. “But by then I was sort of hooked.” He runs the prime-seeking program in the background of the dozen or so computers for which he’s a volunteer network administrator. And, he says, the element of competition is fun.