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 A176840 #4 Jan 20 2014 22:19:36 %S A176840 1,-1,1,-1,1,-1,5,-691,7,-3617,43867,-174611,854513 %N A176840 Variant of A176546 with the sign of the second term switched. %C A176840 Essentially the same as A000367. Also the nonzero entries of A027641. %F A176840 a(n)=A176546(n), n>1. %Y A176840 Cf. A027641. %K A176840 sign,frac,easy,less %O A176840 0,7 %A A176840 _Paul Curtz_, Apr 27 2010