Blog

The biggest ever prime number has just been found and it’s absolutely massive. It’s a number with more than 41 million digits. That means, if you were to type it out in size 12 font, it would stretch 200 km long! That’s about a three hour car ride.

Prime numbers can only be divided by 1 and themselves. For example, 7 is a prime number because only 1 and 7 go into 7 without leaving a remainder. 11 is the next prime number, then 13, 17, 19, 23, 29 and so on. Prime numbers get harder to find the higher you count.

Mathematicians have been trying to understand prime numbers for hundreds of years. One of them was a French monk named Marin Mersenne who lived from 1588–1648 CE.

Mersenne is known today for his attempts to write a formula that would find all primes. He failed in this quest, but he did put forward a simple formula in 1644: take a prime number of 2s and multiply them all together. You’ll get a big number, which definitely isn’t prime. But if you subtract one, you’ll get something that just might be! Primes that are found with this formula are called Mersenne primes.

Mathematicians like to look for these Mersenne primes because there are lots of clever tricks they can use to check them. The largest non-Mersenne prime we’ve discovered has less than 13 million digits, compared to 41 million for this new giant.

No one has found a better method for finding big prime numbers than Mersenne. But multiplying millions of 2s together makes for very large numbers. So, finding bigger and bigger prime numbers has meant that the people looking for them need more and more powerful computers to calculate and check the Mersenne primes.

Enter GIMPS or the Great Internet Mersenne Prime Search. They are a group of volunteers sharing computers and software to find bigger prime numbers. Started in 1996, GIMPS members have found the last 18 Mersenne primes, including this new one.

Did you know that anyone can join GIMPS? You could help discover the next Mersenne prime!

Note: a previous version of this article stated that writing out 41 million digits would stretch from Australia to Japan – but we made a calculation error (see comment below) and have since fixed it.