Prime time for Missouri computing team

A university team has found the largest known prime number, the newest accomplishment from a cooperative computing project.

Stephen Shankland principal writer
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Stephen Shankland
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A Central Missouri State University team using more than 700 computers has found the largest prime number so far, a gargantuan 9,152,052-digit numeral.

The discovery, made Dec. 15 and confirmed Saturday, marked the second time this year that a cooperative computing project called the Great Internet Mersenne Prime Search (GIMPS) has found a new largest prime. But like February's find, it falls short of the 10 million digit size required to earn a $100,000 prize from the Electronic Frontier Foundation.

The GIMPS project harnesses the collective power volunteered by more than 200,000 computers, among which the task of scouring all possible Mersenne primes is divided. Although some prime numbers are used in encryption and other practical tasks, the largest primes are chiefly of academic interest.

A prime number is one that is evenly divisible only by itself and 1, and a Mersenne prime is a particular type that is 1 less than a power of 2. For example, 7 is a Mersenne prime because it's a prime number and is 2 to the third power minus 1.

For several years, the largest primes discovered have been Mersenne primes. They're named after Marin Mersenne, a French monk born in 1588 who investigated the numbers.

Mersenne primes have in many cases been found by individuals, but this time the result came from a team that so far has contributed more processing time than any others--the equivalent of 67,000 years running a 90MHz Pentium computer. Two professors, Curtis Cooper and Steven Boone, lead the university's effort.

The prime discovered this month, the 43rd Mersenne prime found so far, is 2 to the power of 30,402,457 minus 1.

Those who want to see the actual number can download it as a large text file.

Searching for prime numbers is one type of computing task that can be easily divided among many computers, an approach called distributed computing. Other such projects include the SETI@home search for radio signals from intelligent aliens, the Folding@home project to simulate how large biological molecules called proteins are formed, and the Distributed.net project, which tries to crack encryption challenges and find optimal Golomb rulers--a mathematical curiosity that can be useful in several scientific and communication tasks.

The technique has spawned a small industry, though, typically for customers that use distributed computing internally on a smaller scale. For example, pharmaceutical companies and processor designers often put PCs to use after hours, and companies including Parabon Computation, United Devices and Entropia supply software.