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 A294290 #9 Oct 27 2017 10:16:13
%S A294290 1,-1,1,-1,25,-241,1081,-3361,68881,-1288225,11828881,-69917761,
%T A294290 1347298921,-36402297361,533785676425,-4949573821921,96936811739041,
%U A294290 -3274354780495681,67608887254849441,-885780921100074625,18450482854023522361,-718444927697360335921
%N A294290 E.g.f.: exp(1/((1+x)*(1+x^2)) - 1).
%H A294290 Seiichi Manyama, <a href="/A294290/b294290.txt">Table of n, a(n) for n = 0..446</a>
%o A294290 (PARI) N=66; x='x+O('x^N); Vec(serlaplace(exp(1/((1+x)*(1+x^2))-1)))
%Y A294290 Column k=2 of A294289.
%K A294290 sign
%O A294290 0,5
%A A294290 _Seiichi Manyama_, Oct 27 2017