This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A136111 #3 Mar 31 2012 20:02:01 %S A136111 1,575,202605639573839041,478502736827135487987972323577847681 %N A136111 Positive integers n such that for every k in [n,n+1,n+2,n+3,n+4] we have sigma(k) coprime to k. %C A136111 Note that it is impossible to have three consecutive positive even integers which have odd sigma() values. %C A136111 In order to have an odd sigma() value, the integer must be a square or twice a square; it's not too hard to see that three consecutive positive even integers can't each be a square or twice a square. %C A136111 So any solution must have n odd and among n+1 and n+3, one of them must be a square and the other must be twice a square. %C A136111 Any other terms exceed 10^128. %K A136111 nonn %O A136111 1,2 %A A136111 _Jack Brennen_, Mar 17 2008