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 A070990 #8 Feb 28 2017 22:47:03
%S A070990 1,-1,2,-1,1,-2,3,-1,2,-3,3,-2,1,-3,4,-1,3,-4,5,-3,2,-5,5,-2,3,-5,4,
%T A070990 -3,1,-4,5,-1,4,-5,7,-4,3,-7,8,-3,5,-8,7,-5,2,-7,7,-2,5,-7,8,-5,3,-8,
%U A070990 7,-3,4,-7,5,-4,1,-5,6,-1,5,-6,9,-5,4,-9,11,-4,7,-11,10,-7,3,-10,11,-3,8,-11,13,-8,5,-13,12,-5,7,-12,9,-7,2,-9,9,-2,7,-9,12,-7
%N A070990 First differences of A002487.
%F A070990 -a(2n+3) = a(2n) = A002487(n+2), n >= 0. - _Ralf Stephan_, Aug 17 2003
%F A070990 G.f.: -1/x^2 + ((1 - x)/x^2)*Product_{k>=0} (1 + x^(2^k) + x^(2^(k+1))). - _Ilya Gutkovskiy_, Feb 28 2017
%Y A070990 Cf. A002487.
%K A070990 sign
%O A070990 0,3
%A A070990 _N. J. A. Sloane_, May 24 2002