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 A122012 #12 Jul 28 2015 15:36:53
%S A122012 0,3,3,7,9,18,24,47,63,123,165,322,432,843,1131,2207,2961,5778,7752,
%T A122012 15127,20295,39603,53133,103682,139104,271443,364179,710647,953433,
%U A122012 1860498,2496120,4870847,6534927,12752043,17108661,33385282,44791056
%N A122012 G.f.: x^2*(3+3*x-2*x^2)/ ( (x^2-x-1) * (x^2+x-1)).
%H A122012 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (0, 3, 0, -1).
%F A122012 a(n)= 3*a(n-2) -a(n-4).
%F A122012 a(n)= A022096(n-1)/2 + (-1)^n*A000045(n-2)/2, n >1.
%F A122012 a(2n+1)= A099256(2n-2), n>=1. [Mar 27 2010]
%t A122012 M = {{0, 1, 1, 0}, {1, 0, 0, 1}, {1, 0, 0, 0}, {0, 1, 0, 0}} v[1] = {0, 1, 2, 3} v[n_] := v[n] = M.v[n - 1] a = Table[Floor[v[n][[1]]], {n, 1, 50}]
%K A122012 nonn,easy
%O A122012 1,2
%A A122012 _Roger L. Bagula_, Sep 11 2006
%E A122012 Definition replaced with generating function by the Assoc. Eds. of the OEIS, Mar 27 2010