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Originally published Saturday, September 27, 2008 at 12:00 AM

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Elusive prime number discovered by UCLA mathematicians

University of California, Los Angeles, mathematicians appear to have won a $100,000 prize from the Electronic Frontier Foundation (EFF...

Los Angeles Times

University of California, Los Angeles, mathematicians appear to have won a $100,000 prize from the Electronic Frontier Foundation (EFF) for discovering a 12.9-million-digit prime number that has long been sought by computer users.

While the prize money is nothing special, the bragging rights for discovering the 46th known Mersenne prime are huge.

"We're delighted," said UCLA's Edson Smith, leader of the effort. "Now we're looking for the next one, despite the odds." The odds are thought to be about one in 150,000 that any number tested will be a Mersenne prime.

Prime numbers are those, such as three, seven and 11, that are divisible only by themselves and one. Mersenne primes, named after the 17th-century French mathematician Marin Mersenne, who discovered them, take the form of (2 to the power of P )- 1, where P is also a prime number.

In the new UCLA prime, P = 43,112,609.

Thousands of people worldwide 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. The prize was being offered for finding the first Mersenne prime with more than 10 million digits.

Since last autumn, Smith and his UCLA colleagues have harnessed the power of the 75 machines in the university's Program in Computing/Math Computer Lab. Smith, a system administrator, realized the lab was using only a fraction of its available CPU power. Rather than let it go to waste, he and his colleagues decided to use it for the GIMPS project.

The new Mersenne prime was discovered Aug. 23 on a Dell Optiplex 745 running Windows XP. The number was verified by a different computer system running a different algorithm.

The new prime is the eighth Mersenne prime discovered at UCLA.

EFF is an activist group supporting individual rights on the Web. The group established a series of prizes in 1999 to promote cooperative computing on the Web.

The prize will be awarded when the new prime is published, probably next year. By prearrangement, half the money will go to UCLA, one-quarter to charity and the rest to other GIMPS participants and the organization.

Copyright © 2008 The Seattle Times Company

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