The largest prime number yet has been discovered — and it's 17,425,170 digits long. The new prime number crushes the last one discovered in 2008, which was a paltry 12,978,189 digits long. 
 
 The number — 2 raised to the 57,885,161 power minus 1 — was discovered by University of Central Missouri mathematician Curtis Cooper as part of a giant network of volunteer computers devoted to finding primes, similar to projects like SETI@Home, which downloads and analyzes radio telescope data in the Search for Extraterrestrial Intelligence (SETI). The network, called the Great Internet Mersenne Prime Search (GIMPS) harnesses about 360,000 processors operating at 150 trillion calculations per second. This is the third prime number discovered by Cooper. 
 
 "It's analogous to climbing Mt. Everest," said George Woltman, the retired, Orlando, Fla.-based computer scientist who created GIMPS. "People enjoy it for the challenge of the discovery of finding something that's never been known before." 
 
 In addition, the number is the 48th example of a rare class of primes called Mersenne Primes. Mersenne primes take the form of 2 raised to the power of a prime number minus 1. Since they were first described by French monk Marin Mersenne 350 years ago, only 48 of these elusive numbers have been found, including the most recent discovery. [The Most Massive Numbers in the Universe] 
 
 After the prime was discovered, it was double-checked by several other researchers using other computers. 
 
 While the intuitive way to search for primes would be to divide every potential candidate by ever single number smaller than itself, that would be extremely time-consuming, Woltman told LiveScience. 
 
 "If you were to do it that way it would take longer than the age of the universe," he said. 
 
 Instead, mathematicians have devised a much cleverer strategy, that dramatically reduces the time to find primes. That method uses a formula to check much fewer numbers. 
 
 The new discovery makes Cooper elligible for a $3,000 GIMPS research discovery award. 
 
 Follow LiveScience on Twitter @livescience. We're also on Facebook & Google+. ||||| The largest known prime number has just shot up to 257,885,161 - 1, breaking a four-year dry spell in the search for new, ever-larger primes. 
 
 Curtis Cooper at the University of Central Missouri in Warrensburg made the find as part of the Great Internet Mersenne Prime Search (GIMPS), a distributed computing project designed to hunt for a particular kind of prime number first identified in the 17th century. 
 
 All prime numbers can only be divided by themselves and 1. The rare Mersenne primes all have the form 2p - 1, where p is itself a prime number. 
 
 The new prime, which has over 17 million digits, is only the 48th Mersenne prime ever found and the 14th discovered by GIMPS. The previous record holder, 243,112,609 - 1, which was also found by GIMPS in 2008, has just under 13 million digits. All of the top 10 largest known primes are Mersenne primes discovered by GIMPS. Until today, the most recent addition to the list was found in 2009, but it was smaller than the 2008 discovery. 
 
 Volunteer sifters 
 
 Though there are an infinite number of primes, there is no formula for generating these numbers, so discovering them requires intensive computation. GIMPS uses volunteers' computers to sift through each prime-number candidate in turn, until eventually one lucky user discovers a new prime. 
 
 Cooper runs GIMPS software on around a thousand university computers, one of which spent 39 days straight proving that the number was prime. This was then independently verified by other researchers. 
 
 Though there is little mathematical value to finding a single new prime, these rare numbers are prized in their own right by some. "It's sort of like finding a diamond," says Chris Caldwell at the University of Tennessee, Martin, who keeps a record of the largest known primes. "For some reason people decide they like diamonds and so they have a value. People like these large primes and so they also have a value." 
 
 Prime-hunting isn't a completely esoteric pastime though, as these numbers underpin the cryptographic techniques used to make online transactions secure. 
 
 Prizes for primes 
 
 The Electronic Frontier Foundation, an internet civil liberties group, is offering prizes of $150,000 and $250,000 to the discovery of the first prime with at least 100 million and a billion digits, respectively. Previous prizes for primes 1 million and 10 million digits long have already been awarded. 
 
 Cooper will receive a $3000 prize from GIMPS for making the discovery. 
 
 Don't expect to see the next largest prime any time soon though. The problem becomes harder over time, as larger primes are both more rare and harder to check. "Those two things work together to spread them out as time goes on," says Caldwell. 
 
 If you would like to reuse any content from New Scientist, either in print or online, please contact the syndication department first for permission. New Scientist does not own rights to photos, but there are a variety of licensing options available for use of articles and graphics we own the copyright to.
– The Great Internet Mersenne Prime Search just paid dividends in the hunt for ever-bigger prime numbers, the New Scientist reports. University of Central Missouri mathematician Curtis Cooper has discovered the biggest prime number yet, a 17 million-digit behemoth, as part of GIMPS. The project uses a huge network of volunteer computers as part of the search for Mersenne primes, a rare type of prime number first noted in the 17th century. The number—2 raised to the power of 57,885,161 minus 1—is more than 4 million digits longer than the previous record holder, which was found in 2008, LiveScience adds. So what is the giant number good for? Large primes can be used for online encryption, but mathematicians say it's mostly about the thrill of the hunt. "People enjoy it for the challenge of the discovery of finding something that's never been known before," the computer scientist who created GIMPS says. Cooper also wins $3,000 for the discovery, but a bigger payday looms. The Electronic Frontier Foundation will award $150,000 to the person who finds a prime with 100 million digits; a one billion-digit find returns a $250,000 prize.