UCLA Researchers Discover a Prime Number With 13 Million Digits

Mathematics researchers at the University of California at Los Angeles have discovered the largest known prime number — a 13-million-digit behemoth — almost a year after setting up 75 computer-lab PC’s to work on the search in their spare time. The researchers are believed to have won a $100,000 prize offered by the Electronic Frontier Foundation for the discovery of the first prime number of more than 10 million digits.

According to the Great Internet Mersenne Prime Search, a project that has harnessed excess computing power of machines around the world to carry out the search, a UCLA computer discovered the number on August 23. A Mersenne prime takes the form 2P-1, and UCLA’s — the 45th known Mersenne prime — is 243,112,609-1. The Los Angeles Times says the number was discovered by a Dell Optiplex 745 running the project’s software on Windows XP.

Project officials say that Mersenne primes are not themselves useful, but that the search “has proved useful in development of new algorithms, testing computer hardware, and interesting young students in math.” The 46th known Mersenne prime, with just over 11 million digits, was discovered just two weeks after the UCLA number by a prime-number enthusiast’s computer in Germany.

The search for a Mersenne prime with more than 10 million digits had been under way since 1996 and involved as many as 100,000 machines. The next challenge — for which a $150,000 reward is being offered — is the discovery of a 100-million-digit prime. —Lawrence Biemiller

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