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 A118408 #5 Dec 23 2024 10:17:58
%S A118408 1,1,-1,1,1,-1,3,-3,1,7,-13,13,1,-25,51,-51,1,103,-205,205,1,-409,819,
%T A118408 -819,1,1639,-3277,3277,1,-6553,13107,-13107,1,26215,-52429,52429,1,
%U A118408 -104857,209715,-209715,1,419431,-838861,838861,1,-1677721,3355443,-3355443,1,6710887,-13421773,13421773,1
%N A118408 Row sums of triangle A118407.
%H A118408 <a href="/index/Rec#order_05">Index entries for linear recurrences with constant coefficients</a>, signature (-1, -1, 1, 0, 2).
%F A118408 G.f.: (1+x)^2/(1+x^2)/(1+2*x+2*x^2)/(1-x).
%o A118408 (PARI) {a(n)=polcoeff((1+x)^2/(1+x^2)/(1+2*x+2*x^2)/(1-x+x*O(x^n)),n)}
%Y A118408 Cf. A118407 (triangle), A118409 (unsigned row sums).
%K A118408 sign
%O A118408 0,7
%A A118408 _Paul D. Hanna_, Apr 27 2006