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 A099487 #6 Jun 13 2015 00:51:33
%S A099487 1,1,3,14,53,195,727,2716,10137,37829,141179,526890,1966381,7338631,
%T A099487 27388143,102213944,381467633,1423656585,5313158707,19828978246,
%U A099487 74002754277,276182038859,1030725401159,3846719565780,14356152861961
%N A099487 Expansion of (1-3x+x^2)/((1+x^2)(1-4x+x^2)).
%C A099487 A Chebyshev transform of the sequence 1,1,4,16.. which has with g.f. (1-3x)/(1-4x). The image of G(x) under the Chebyshev transform is (1/(1+x^2))G(x/(1+x^2)).
%H A099487 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (4,-2,4,-1).
%F A099487 a(n)=4a(n-1)-2a(n-2)+4a(n-3); a(n)=sum{k=0..floor(n/2), C(n-k, k)(-1)^n*(4^(n-2k)+3*0^(n-2k))/4}.
%Y A099487 Cf. A099486, A099488.
%K A099487 easy,nonn
%O A099487 0,3
%A A099487 _Paul Barry_, Oct 18 2004