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 A099214 #4 Mar 30 2012 18:59:00
%S A099214 1,2,4,12,40,128,400,1248,3904,12224,38272,119808,375040,1174016,
%T A099214 3675136,11504640,36014080,112738304,352915456,1104764928,3458351104,
%U A099214 10826006528,33889681408,106088103936,332097716224,1039597174784
%N A099214 a(n)=4a(n-1)-4a(n-2)+4a(n-3).
%C A099214 Binomial transform of A099213.
%F A099214 G.f.: (1-2x)/((1-2x)^2-4x^3); a(n)=sum{k=0..floor(n/3), binomial(n-k, 2k)4^k*2^(n-3k)}.
%Y A099214 Cf. A073724.
%K A099214 easy,nonn
%O A099214 0,2
%A A099214 _Paul Barry_, Oct 06 2004