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 A093546 #10 Aug 02 2016 17:40:50 %S A093546 1,3,9,27,57,81,171,243,513,729,1083,1467,1539,2187,3249,4401,4617, %T A093546 6561,9747,13203,13851,19683,20577,27873,29241,32547,39393,39609, %U A093546 41553,59049,61731,83619,87723,97641,118179,118827,124659,177147,185193,239121 %N A093546 Numbers n such that n divides 2^n^2 + 1. %C A093546 This sequence is closed under multiplication. A006521 is a subsequence of this sequence. A006521 is also closed under multiplication. In fact if m is even and k is a natural number then the sequence "n divides m^n^k + 1" is a subsequence of the sequence "n divides m^n^(k+1)+ 1" and both are closed under multiplication. %C A093546 "Closed under multiplication" means that if x and y are terms then so is x*y. %H A093546 Charles R Greathouse IV, <a href="/A093546/b093546.txt">Table of n, a(n) for n = 1..415</a> %t A093546 Select[ Range[250857], PowerMod[2, #^2, # ] == # - 1 &] (* _Robert G. Wilson v_, Apr 02 2004 *) %o A093546 (PARI) is(n)=Mod(2,n)^n^2==-1 \\ _Charles R Greathouse IV_, Aug 01 2016 %Y A093546 Cf. A006521, A067945, A093547. %K A093546 nonn %O A093546 1,2 %A A093546 _Farideh Firoozbakht_, Mar 31 2004 %E A093546 Corrected and extended by _Robert G. Wilson v_, Apr 02 2004