In 1991, Harvey Dubner discovered a prime with a total of 6,400 digits: all 9s except one 8 Posted on 2020/10/21 by Carl Robitaille In 1991, Harvey Dubner discovered a prime with a total of 6,400 digits: all 9s except one 8. Here's the precise value pic.twitter.com/huJHxCeo2d— Fermat's Library (@fermatslibrary) October 21, 2020