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Late last year, Jonathan Pace’s computer found something special. Jonathan is an electrical engineer who also manages computers for charities, so he has a lot of computers, but this one was nothing out of the ordinary. Except for one thing: the computer was running software from the Great Internet Mersenne Prime Search, an international volunteer group on the hunt for giant primes.

For six days, this computer analysed a very large number, doing calculation after calculation, trying to find a number that would divide into it without leaving a remainder. Eventually, it ran out of divisors to check. The very large number couldn’t be made by multiplying smaller whole number together. It was a prime number.

There are plenty of prime numbers out there, and one of the earliest facts ever discovered about prime numbers was that they never end. No matter how big a prime number you find, there are always bigger ones to discover.

Jonathan’s prime is special because it’s the largest prime ever found, with 23 249 425 digits. If you printed Jonathan’s prime in a book, it would have around 5200 pages. That’s more pages than all the Harry Potter books, plus The Hunger Games trilogy combined!

This newly discovered prime is so big it’s hard to imagine. It’s larger than the number of stars in the sky, and larger than the number of atoms in the ocean. If you packed the entire observable universe with atoms as tight as you possibly could, that number would only have around 180 digits – only about three lines on one page of a book!

Although Jonathan’s prime number is the largest we’ve ever discovered, we know there are even larger ones out there. And there’s plenty of incentive to look. The first person to discover a prime number with more than 100 million digits will win a $150 000 prize!

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