Mathematicians at UCLA believe they have found a very long and very special prime number: It clocks in at nearly 13 million digits, and belongs to an elite group of numbers called Mersenne primes. If the math checks out, the discovery will win UCLA's math department a $100,000 prize that was offered for the first Mersenne prime found with over 10 million digits.

Primes are numbers like three, seven and 11 that are divisible by only two whole positive numbers: themselves and one. Mersenne primes — named for their discoverer, 17th century French mathematician Marin Mersenne — are expressed as 2^P-1, or two to the power of "P'' minus one. P is itself a prime number. For the new prime, P is 43,112,609 [AP].

Thousands of people around the world have been participating in the Great Internet Mersenne Prime Search, or GIMPS, in which underused computing power is harnessed to perform the complex and tedious calculations needed to find and verify Mersenne primes [Los Angeles Times].

Edson Smith of UCLA got involved last fall by downloading the GIMPS software for the 75 machines in the university's math computer lab; when the computers weren't busy with other work, they searched for Mersenne primes and sent their results back to GIMPS. A computer found that magic number on August 23rd, and it was just in time.

Remarkably, GIMPS found another Mersenne prime two weeks after this one – after a two-year dry spell with no new primes [Science News].

This newest prime number, which has about 11 million digits, was discovered by a German engineer who GIMPS describes as "a prime number enthusiast." The prize is offered by the Electronic Frontier Foundation, a nonprofit group that set up the competition to promote "cooperative computing." The prize will be awarded to the UCLA math department once the new prime is published in an academic journal.

People aren't hunting for Mersenne primes in order to prove anything about them, according to Mike Breen of the American Mathematical Society. "They're doing it because it's there, and it's an interesting challenge," he says. Math nerds also go ga-ga for really big numbers, as we all do I'm sure [Scientific American].

For another party trick that mathematicians like to perform with prime numbers, check out the DISCOVER article "Prime-Time News." Image: iStockphoto