Largest known prime number - 17M digits long - discovered

Typed out in Times Roman 12 point font, number would stretch more than 30 miles or fill more than six Bibles

A mathematician at the University of Central Missouri has discovered what is now the largest known prime number -- one with more than 17 million digits.

Dr. Curtis Cooper, who has made two other prime number discoveries, has found the 48th known Mersenne prime -- 257,885,161 minus 1. The number is 17,425,170 digits long.

Cooper discovered the number on Jan. 25, according to the Great Internet Mersenne Prime Search (GIMPS), a 16-year-old project that uses a grid of computers provided by volunteers to find large prime numbers.

If the number was typed out in standard Times Roman 12 point font, it would span more than 30 miles. It also would fill more than six Bibles.

A prime number is a whole number that can be divided only by one and itself. Mersenne prime numbers are a class of primes named after Marin Mersenne, a 17th century French monk who studied the rare numbers more than 350 years ago. Mersenne primes are extremely rare. With this discovery, only 48 are known.

Each Mersenne prime is increasingly difficult to find.

GIMPS noted that the grid that Cooper used for the discovery had 360,000 CPUs peaking at 150 trillion calculations per second.

According to GIMPS, the first time Cooper discovered a record-breaking prime number was 2005. His second came quickly after in in 2006.

However, mathematicians at UCLA broke Cooper's record in 2008. That record Mersenne prime number held until Cooper and the University of Central Missouri reclaimed it with this latest discovery.

To verify the new Mersenne prime number, it was independently tested using different programs running on different hardware, GIMPS noted. One verification test, which lasted 3.6 days, used a Nvidia GPU, while another used an Intel Core i7 CPU and lasted four and a half days.

Sharon Gaudin covers the Internet and Web 2.0, emerging technologies, and desktop and laptop chips for Computerworld. Follow Sharon on Twitter at  @sgaudin, on Google+ or subscribe to Sharon's RSS feed . Her email address is sgaudin@computerworld.com.

See more by Sharon Gaudin on Computerworld.com.

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