Michael Shafer said he felt like he won the lottery on Nov. 17 after reading the computer screen in his Engineering Building office that said, "New Mersenne prime found."

The 26-year-old chemical engineering graduate student's name instantaneously hit the record books as the person who discovered the largest prime number known to man. A prime number is a positive number only divisible by one and itself.

"After I found out, I did a short victory dance," Shafer said. "I'm glad no one was around watching.

"This is like winning the lottery. Someone would have found the number if I didn't."

The number is 2 to the 20,996,011th power minus 1 and, if looked at in its entirety, is 6,320,430 digits long - breaking a two-year record of the largest prime number.

Shafer said a Mersenne prime is a prime expressed as 2 to the "p" power minus 1; p also must be a prime for it to be considered rare.

The number would take about 1,500 pages to write.

Shafer made the discovery by participating in a project called the "Great Internet Mersenne Prime Search," more commonly known as GIMPS.

Shafer ran his computer for 19 days straight, but it took about two weeks before the number could officially be verified as the largest prime number.

Shafer said most of the credit for the discovery should be given to creators of the program.

"I was the fortunate one to get this particular number to search," he said. "It could be next week, it could be five years from now. This group will find another prime number; it's just a matter of time."

Shafer, who has been a member of the project for three years, is one of 60,000 people who use 211,000 computers of varying capabilities to run software that is connected through one server.

San Diego resident and creator of the server Scott Kurowski said the server and software enables participants to fuse computer capabilities and essentially turn the program into a supercomputer. The supercomputer could then perform 9 trillion calculations per second.

"It's a project that's bigger than life for a lot of participants," he said. "It's important motivation to be involved in something worldwide and history making."

Kurowski said the GIMPS program has made about six important discoveries on prime numbers. A new record breaks at a rate of about every two years.

Kurowski added there is a non-profit organization called the Electronic Frontier Foundation, offering $100,000 to the discoverer of a 10,000,000 digit prime number.

Chris Caldwell, professor of mathematics and statistics at the University of Tennessee at Martin, said Shafer's discovery is important because it is only the 40th Mersenne prime ever found. Caldwell also is the founding editor of The Prime Pages, an Internet site that stores the largest primes known and the people who discovered them.

Caldwell said those outside the field sometimes don't have a good understanding of what a prime number is.

"Most of the primes that are known are the small ones," he said. "What makes this thing beautiful is just how big this thing is.

"It's just so big; it almost defies physical meaning."

Prime numbers of less than 1,000 digits are normally used for cryptographic coding, commonly used by the military, banks and to secure sites on the Internet, Caldwell said.

He added there is only theoretical work on prime numbers the size of Shafer's discovery but that time might change that.

"It's mostly for bragging rights," Caldwell said. "Mathematics will still be the same tomorrow morning."

Shafer said he has received mix reaction from family and friends about his newfound fame.

"One guy said I deserved a wedgie," he said. "Other people are talking about world domination."

The Associated Press contributed to this report.

Antonio Planas can be reached at planasan@msu.edu.