A University of Central Missouri professor has discovered a 17 million digit prime number, far exceeding the previous record of just under 13 million digits.

The number in question is 2 to the power of 57,885,161 minus 1. It’s so big that a file containing the number takes up 22.5MB.

It was discovered by Dr Curtis Cooper who previously broke the record in 2005 and 2006. He held it until 2008 when UCLA set a record that stood until this week.

Cooper found the number as part of a collaborative effort known as the Great Internet Mersenne Prime Search (GIMPS). It works on the basis that finding prime numbers is a task perfectly suited to combining the power of multiple computers. The project makes use of around 360,000 processors in total.

It took 39 days for a computer at Cooper’s university to confirm the number was a prime. Two other people independently verified the number using more powerful computers, taking several days apiece.

Although the prime has been confirmed, it’s too early yet to confirm its place in listings of prime number. That will mean checking every number between the new and previous record holders to rule them out as primes, a process that’s likely to be measured in years rather than months.

Cooper gets a $3,000 prize from GIMPS because it was his computer that found the new prime. He’s someway short of a much larger prize from the Electronic Frontier Foundation which has offered $150,000 to the first person to find a prime with 100 million digits and then $250,000 when the 1 billion digit mark is reached. It has already paid out smaller prizes for a million and 10 million digit primes.

Prime numbers aren’t just a lovable quirk for geeks to pursue. RSA security, used widely in computer data encryption, is based on the fact that its easy to multiply two prime numbers (components) together to produce a larger number (composite) but extremely time consuming and difficult to take the composite and figure out the two components that created it.