Thread: 3, 7, 31, 127 View Single Post
 2019-04-03, 17:52 #5 petrw1 1976 Toyota Corona years forever!     "Wayne" Nov 2006 Saskatchewan, Canada 23×5×112 Posts I thought this was too easy The only 4 numbers so far that are: - exponents of MPs - an MP 7 for example: $2^3-1 = 7$ and $2^7-1 = 31$ The next candidate may be a few years away: (TEX wasn't behaving here) 231 = 2147483647 22147483647 -1 = xxx Is xxx a prime?