[math-fun] A prime factor of the Fermat number F22

Someone has just found a 35-digit prime factor of F22. This is less than two months after a factor of F14 was discovered. The cofactor is composite. See http://mersenneforum.org/showthread.php?p=209627 Now F20 and F24 are the only known composite Fermat numbers without any known prime factors. Warut