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 A099216 #6 Jun 13 2015 00:51:32
%S A099216 1,2,4,10,28,80,228,648,1840,5224,14832,42112,119568,339488,963904,
%T A099216 2736800,7770560,22062848,62642752,177860736,504997632,1433833088,
%U A099216 4071063296,11558916096,32819077376,93182771712,264572609536
%N A099216 a(n)=4a(n-1)-4a(n-2)+2a(n-3).
%C A099216 Binomial transform of tribonacci numbers A000213.
%H A099216 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (4,-4,2).
%F A099216 G.f.: (1-2x)/((1-2x)^2-2x^3); a(n)=sum{k=0..floor(n/3), binomial(n-k, 2k)2^k*2^(n-3k)}.
%Y A099216 Cf. A099214, A099215, A055588.
%K A099216 easy,nonn
%O A099216 0,2
%A A099216 _Paul Barry_, Oct 06 2004