The largest known prime number is actually : 2^(32,582,657)â?? 1. It has 9,808,358 digits. I don't know about this prime, but the second largest prime number, 6,320,430 digits long, took just over two years to find using a distributed network of more than 200,000 computers! (http://www.newscientist.com/article/dn4438.html)