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 A099493 #6 Jun 13 2015 00:51:33
%S A099493 1,0,1,2,-1,0,3,-4,-3,8,-7,-10,23,-8,-33,56,1,-104,121,58,-297,232,
%T A099493 291,-780,349,1072,-1903,174,3407,-4272,-1505,9840,-8543,-8752,26321,
%U A099493 -13902,-33777,65456,-11805,-110356,150173,35192,-325303,310054,257319,-885496,537919,1054888,-2240927
%N A099493 Expansion of (1+x^2)^2/(1+x^2-2x^3+x^4+x^6).
%C A099493 A Chebyshev transform of A052907, which has g.f. 1/(1-2x^2-2x^3). The image of G(x) under the Chebyshev transform is (1/(1+x^2))G(x/(1+x^2)).
%H A099493 <a href="/index/Rec#order_06">Index entries for linear recurrences with constant coefficients</a>, signature (0,-1,2,-1,0,-1).
%F A099493 a(n)=-a(n-2)+2a(n-3)-a(n-4)-a(n-6); a(n)=sum{k=0..floor(n/2), C(n-k, k)(-1)^k*sum{j=0.., floor(n-2k/2), C(j, n-2k-2j)2^j}}.
%K A099493 easy,sign
%O A099493 0,4
%A A099493 _Paul Barry_, Oct 19 2004