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The Sciences

Largest Known Prime Number Finally Found

Researcher discovered the largest known prime number, and it is 6,320,430 digits long.

By Alex StoneMarch 28, 2004 6:00 AM

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After two years of work, a Web-based network of more than 60,000 math enthusiasts has uncovered the largest known prime number, a staggering 6,320,430 digits long. (We’d print it, but it would fill about 1,000 pages.) The volunteers, using a total of 200,000 computers, were assigned potential primes to test as part of an international project started by American computer scientist George Woltman in 1996. The winning computer was a Dell Pentium 4 in the office of Michael Shafer, a chemical engineering graduate student at Michigan State University.

Prime numbers—integers that are divisible only by one and themselves—have important practical applications, including the creation of public encryption keys that safeguard online bank transactions. The newest prime has an added distinction: It is what is known as a Mersenne prime. These rare numbers, discovered by Euclid in 350 B.C., can be written using the formula 2^p – 1, where p is also a prime number. (In this case p equals 20,996,011.) Most prime numbers cannot be written this way. In fact, the newly discovered prime is only the 40th of its kind to be found. “It was pretty exciting,” Shafer says. “In a way it’s like winning the lottery.”

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