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U.S. professor finds longest prime number with 17,425,170 digits

By Kevin Murphy | Reuters Fri, Feb 8, 2013

KANSAS CITY, Missouri (Reuters) - After running 1,000 computers non-stop for 39

days to uncover the world's largest prime number yet, a Missouri college

professor said this week he is starting all over to top his own record.

"It's a never-ending job," said Curtis Cooper, a computer science professor at

the University of Central Missouri in Warrensburg. The computers are still

running, although finding a higher prime number is estimated to take five to

seven more years. Thousands of other computers in the United States are making

the same search.

"This is my first love," Cooper, 60, said in an interview with Reuters. "It's

pure mathematics. It's kind of an art form."

Cooper said he has received calls and emails from around the world after

Wednesday's announcement that he had identified the prime number - which is a

number that can only be divided by itself and 1. For example, 4 is not a prime

number because it can be divided by itself, 1 and 2. Prime numbers include 2,

3, 5, 7 and on up to the giant figure Cooper and his computers discovered,

which has 17,425,170 digits.

The new number is 2 multiplied by itself 57,885,161 times, minus 1. A single

campus computer, labeled #22, found the number on January 25, but it had to be

verified by the prime number locator project known as GIMPS - the Great

Internet Mersenne Prime Search.

The term "Mersenne" refers to the rarest prime numbers, only 48 in all, that

have ever been discovered. GIMPS has discovered the last 14 of them.

Working with the GIMPS system, Cooper and Central Missouri chemistry professor

Steven Boone discovered two earlier record prime numbers, in 2005 and 2006.

Their newest prime number is the largest discovered since 2008, at the

University of California-Los Angeles. It beat the UCLA number by some 5 million

digits.

Having the record prime number discovered three times at Central Missouri, a

state college with about 11,000 students, is a source of great pride, said Mike

Greife, the school's news bureau director. "It's kind of mind-boggling," Greife

said of the search process.

Cooper said his earlier successes finding the highest prime number motivated

him to keep trying. He said he spent at least two hours a day "baby-sitting"

the college computers to make sure everything was operating properly. The

search software runs in the background while the computers carry out other

functions.

Cooper said prime numbers are mostly of interest to mathematicians, but the

search has some practical uses. For one thing, it shows how computers can be

used together on such a project, he said.

Prime numbers also have been used in Web applications to encrypt messages

because they are so rare. Those numbers, though, have a mere 100 to 200 digits,

Cooper said.

(Reporting by Kevin Murphy; Editing by Mary Wisniewski, Greg McCune and Dale

Hudson)