CNN  Thursday, December 11, 2003 Posted: 10:24 AM EST (1524 GMT)

A handful of the 6.3 million digits in the newly discovered
prime number 
DETROIT,
Michigan (AP)  More than 200,000 computers spent years looking for the largest
known prime number. It turned up on Michigan State University graduate student
Michael Shafer's offtheshelf PC.
"It was just a matter of time," Shafer said.
The
number is 6,320,430 digits long and would need 1,400 to 1,500 pages to write
out. It is more than 2 million digits larger than the previous largest known
prime number.
Shafer,
26, helped find the number as a volunteer on an eightyearold project called
the Great Internet Mersenne Prime Search.
Tens of
thousands of people volunteered the use of their PCs in a worldwide project
that harnessed the power of 211,000 computers, in effect creating a
supercomputer capable of performing 9 trillion calculations per second.
Participants could run the mathematical analysis program on their computers in
the background, as they worked on other tasks.


Shafer
ran an ordinary Dell computer in his office for 19 days until November 17, when
he glanced at the screen and saw "New Mersenne prime found."
A prime
number is a positive number divisible only by itself and one: 2, 3, 5, 7 and so
on. Mersenne primes are a special category, expressed as 2 to the "p"
power minus 1, where "p" also is a prime number.
In the
case of Shafer's discovery, it was 2 to the 20,996,011th power minus 1. The
find was independently verified by other participants in the project.
Mersenne primes are rare but are critical to the branch of mathematics
called number theory. That said, what is the practical significance of Shafer's
number?