Re: [math-fun] Prime factors of 10^N + 1

10^20 + 1 is too large for my software

Forget your computer software for this kind of stuff. The website factordb.com is a factor database. http://factordb.com/index.php?query=10%5En%2B1&use=n&n=1&VP=on&VC=on&EV=on&O... That's 10^n+1 up to n=200. Click "next page" to get the next 200. Note that n=311 is the first one that still has an unfactored composite.