An MSU graduate student has harnessed the power of the PC to discover the largest known prime number. The number is 6,320,430 digits long, and took just more than two years to find using a distributed network of 60,000 volunteers’ computers around the world.

Michael Shafer, a chemical engineering student, used his campus office PC to contribute spare processing power to the Great Internet Mersenne Prime Search, known as GIMPS. While the discovery might be a prime target for math anxiety jokes, Shafer noted the project isn’t an oversized math test. Rather, it’s a way to combine the excess computing power sitting on many home and office desks.

“People don’t have to be computer whizzes or math whizzes,” Shafer said. “Anybody can do this project. That’s what makes it exciting. We can get so much more work done with networking projects such as this.”

The new number is expressed as 2 to the 20,996,011th power minus 1. It is more than two million digits larger than the previous largest known prime number, and belongs to a special class of rare prime numbers called Mersenne primes.

Prime numbers are positive integers that can only be divided by themselves and one. Mersenne primes are an especially rare type of prime that take the form 2^p – 1, where p is also a prime number. The new number can be represented as 2^20996011. It is only the 40th Mersenne prime ever to have been found.

Shafer used a free software program as part of an international grid of 211,000 networked computers in virtually every time zone of the world.

“I had just finished a meeting with my adviser when I saw the computer had found the new prime,” he said. “After a short victory dance, I called up my wife and friends involved with GIMPS to share the great news!”

He used a 2 Ghz Pentium 4 Dell Dimension PC running for 19 days to prove the number prime. “The software runs great without affecting the computer,” Shafer said. “I get my work done and contribute to the project at the same time.”

Shafer’s discovery was made Nov. 17, but it was not independently verified until this week.

Shafer, who grew up in DeWitt, Mich., participates in research involved with green chemistry — seeking alternatives to petroleum-based projects.