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 A099526 #6 Jun 13 2015 00:51:34
%S A099526 1,2,4,8,19,44,100,224,505,1142,2584,5840,13195,29816,67384,152288,
%T A099526 344161,777770,1757692,3972248,8976979,20287268,45847612,103611968,
%U A099526 234154873,529171550,1195885936,2702607776,6107680171,13802874992
%N A099526 Expansion of 1/(1-2x-3x^4).
%C A099526 In general 1/(1-a*x-b*x^4) expands to sum{k=0..floor(n/4),C(n-3k,k)b^(n-3k)(a/b)^(n-4k)}.
%H A099526 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (2,0,0,3).
%F A099526 a(n)=2a(n-1)+3a(n-4); a(n)=sum{k=0..floor(n/4), binomial(n-3k, k)3^(n-3k)(2/3)^(n-4k)}.
%Y A099526 Cf. A099525.
%K A099526 easy,nonn
%O A099526 0,2
%A A099526 _Paul Barry_, Oct 20 2004