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Mathematician: Finding 17M-digit prime number like climbing Everest

Computer that discovered latest Mersenne prime did 57M calculations over 39 days

February 6, 2013 04:14 PM ET

Computerworld - The mathematician who found the largest known prime number said the discovery last month was like climbing Mount Everest or landing on the moon.

Curtis Cooper, a mathematician
Curtis Cooper, a mathematician and professor at the University of Central Missouri, stands at the Dell desktop where he discovered the largest known prime number. The computer was one of more than 1,000 computers used in the search. (Photo: University of Central Missouri)

The prime number, which is more than 17 million digits long, won't make computers run faster or help scientists develop better rockets. However, searching for the number was an exhilarating journey for Curtis Cooper, a mathematician at the University of Central Missouri.

If this prime number --2 57,885,161 minus 1, or 2 to the power of 57,885,161 minus 1 - was typed out in a standard Times Roman 12-point font, it would span more than 30 miles. It also would fill more than six Bibles.

It is the third prime number discovery he has made, and Cooper said the discovery isn't any less exciting. He said the feat, for a mathematician, was like climbing Mount Everest, because it was a goal he set out to achieve because he wanted to, not because he needed to.

"We've been working on this for years," Cooper told Computerworld. "We probably finish 50, 60 or 70 numbers per day, and for years we didn't find anything. Then on Jan. 25 we hit the jackpot. It's truly like looking for a needle in a haystack."

The Great Internet Mersenne Prime Search (GIMPS), a 16-year-old project that uses a grid of computers provided by volunteers to find large prime numbers, announced Tuesday that Cooper discovered the 48th known Mersenne prime.

A prime number is a whole number that can be divided only by one and itself. A Mersenne prime number is a class of primes named after Marin Mersenne, a 17th century French monk who studied the rare numbers more than 350 years ago.

Mersenne primes are extremely rare. With this discovery, only 48 are known. Each Mersenne prime is increasingly difficult to find.

Mersenne Primes are 2 raised to the x power, minus 1. For instance, the number 3 is a Mersenne prime number because it can be written as 2 squared, minus one. Number 7 is also a Mersenne prime number because it's 2 cubed, minus one.

To find this new Mersenne prime, Cooper used 1,000 computers on his university campus in Warrensburg, Mo. Each computer checked individual numbers. Dual-core machines could check two numbers at once.

The computer that discovered this 17 million-digit prime is a Dell desktop running an Intel dual-core processor. Sitting in the university's modern language lab, the computer spent 39 days running 57 million calculations to test the number.

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