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 A099431 #6 Jun 13 2015 00:51:33
%S A099431 0,1,0,6,8,30,60,154,336,774,1700,3762,8184,17758,38220,81930,174752,
%T A099431 371382,786420,1660258,3495240,7340046,15379100,32156346,67108848,
%U A099431 139810150,290805060,603979794,1252698776,2594876094,5368709100
%N A099431 Expansion of x(1-2x+3x^2)/(1-x-2x)^2;.
%C A099431 Convolution of A078008 and A099430(n-1)+3*0^n/2.
%H A099431 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (2,3,-4,-4).
%F A099431 a(n)=sum{k=0..n, (2^(n-k)+2(-1)^(n-k))/3*(2^(k-1)-(-1)^k-1+3*0^k/20)}; a(n)=sum{k=0..n+1, A078008(n-k)binomial(n-k+1, k)binomial(1, (k+1)/2)(1-(-1)^k)/2}.
%K A099431 easy,nonn
%O A099431 0,4
%A A099431 _Paul Barry_, Oct 15 2004