GIMPS Discovers 48th Mersenne Prime, 257,885,161-1 is now the Largest Known Prime. ORLANDO, Florida, February 5, 2013 — On January 25th at 23:30:26 UTC, the largest known prime number, 257,885,161-1, was discovered on Great Internet Mersenne Prime Search (GIMPS) volunteer Curtis Cooper's computer. The new prime number, 2 multiplied by itself 57,885,161 times, less one, has 17,425,170 digits (warni