A computer in Missouri has discovered the largest known prime number, 274,207,281– 1. It is about 22 million digits long, 5 million digits longer than the previous largest known prime, which was discovered in January 2013.
Prime numbers are numbers that are divisible only by themselves and one, such as 2, 3, 5, 7, 11 and 13. The search for the highest known prime is a long-established mathematical quest, of interest now more as a test of computing power rather than for any practical use of the number itself. It’s a fun challenge too.
Primes that can be written as one less than a power of two, i.e 2n – 1 for some n, are known as Mersenne primes after the French monk Marin Mersenne who investigated their properties 350 years ago. They are the easiest large primes to find since they provide numbers to aim for, and there’s a quick way to test they are prime.