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 A108486 #5 Jun 13 2015 00:51:50
%S A108486 1,2,10,80,412,2456,14680,85376,503056,2959136,17381536,102199040,
%T A108486 600757696,3531251072,20758107520,122021457920,717273440512,
%U A108486 4216334967296,24784750512640,145691471876096,856414086962176
%N A108486 Sum binomial(2n-2k,2k)3^k*2^(n-k), k=0..floor(n/2).
%C A108486 In general, sum{k=0..floor(n/2), C(2n-2k,2k)a^k*b^(n-k)} has expansion (1-bx-abx^2)/(1-2bx-(2ab-b^2)x^2-2ab^2*x^3+(ab)^2*x^4).
%H A108486 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (4,8,24,-36).
%F A108486 G.f.: (1-2x-6x^2)/(1-4x-8x^2-24x^3+36x^4); a(n)=4a(n-1)+8a(n-2)+24a(n-3)-36a(n-4).
%K A108486 easy,nonn
%O A108486 0,2
%A A108486 _Paul Barry_, Jun 04 2005