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 A165581 #5 Aug 06 2012 16:33:49 %S A165581 0,1,1,-1,1,-1,-1,-1,1,1,-1,-1,-1,1,-1,1,1,-1,1,-1,-1,1,-1,-1,-1,1,1, %T A165581 -1,-1,1,1,1,1,1,-1,1,1,1,-1,-1,-1,1,1,-1,-1,-1,-1,-1,-1,1,1,1,1,1,-1, %U A165581 1,-1,1,1,1,1,-1,1,-1,1,-1,1,1,-1,1,1,1,1,1,1,-1,-1,1,-1,1,-1,1,1,-1 %N A165581 Legendre symbol (n,524287). %C A165581 524287 is the 7th Mersenne prime, A000668(7) = 2^19 - 1. %C A165581 Periodic with period 524287. - _Charles R Greathouse IV_, Aug 06 2012 %H A165581 A. Karttunen, <a href="/A165581/b165581.txt">Table of n, a(n) for n = 0..524287</a> %o A165581 (PARI) a(n)=kronecker(n,524287) \\ _Charles R Greathouse IV_, Aug 06 2012 %Y A165581 Partial sums: A165582. %K A165581 sign,mult,easy %O A165581 0,1 %A A165581 _Antti Karttunen_, Sep 22 2009