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 A097116 #5 Oct 01 2023 18:15:48
%S A097116 1,1,1,4,10,19,40,91,199,427,928,2026,4405,9568,20809,45265,98425,
%T A097116 214012,465394,1012051,2200744,4785619,10406647,22629907,49210024,
%U A097116 107010082,232699861,506019712,1100369809,2392819489,5203328305
%N A097116 Expansion of (1-x)/((1-x)^2-3x^3).
%H A097116 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (2, -1, 3).
%F A097116 G.f. : (1-x)/(1-2x+x^2-3x^3); a(n)=2a(n-1)-a(n-2)+3a(n-3); a(n)=sum{k=0..floor(n/2), binomial(n-k, 2k)3^k }.
%K A097116 easy,nonn
%O A097116 0,4
%A A097116 _Paul Barry_, Jul 25 2004