The 22 million digit number and the amazing maths behind primes January 21, 2016 by Steve Humble, The Conversation Primes: here be magic. Credit: Shutterstock It is a quite extraordinary figure. Dr Curtis Cooper from the University of Central Missouri has found the largest-known prime number - written (274207281)-1. It is around 22m digits long and, if printed in full, would take you days to read. Its discovery comes thanks to a collaborative project of volunteers who use freely available software called GIMPS (Great Internet Mersenne Prime Search) to search for primes. A number which can only be divided by...