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 A038989 #24 Sep 13 2018 11:27:38
%S A038989 1,2,5,14,41,118,341,986,2849,8234,23797,68774,198761,574430,1660133,
%T A038989 4797874,13866113,40073810,115815461,334712894,967338217,2795659334,
%U A038989 8079605429,23350493066,67484177441,195032892538,563655520661,1628994688214,4707882025385
%N A038989 Expansion of (1 - x^2 - 2*x^3) / (1 - 2*x - 2*x^2 - 2*x^3 + x^4).
%H A038989 Colin Barker, <a href="/A038989/b038989.txt">Table of n, a(n) for n = 0..1000</a>
%H A038989 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (2,2,2,-1).
%F A038989 a(n) = 2*a(n-1) + 2*a(n-2) + 2*a(n-3) - a(n-4) for n>3. - _Colin Barker_, Jul 16 2017
%F A038989 Lim_{n -> inf} a(n)/a(n-1) = A318605. - _A.H.M. Smeets_, Sep 12 2018
%p A038989 seq(coeff(series((1-x^2-2*x^3)/(1-2*x-2*x^2-2*x^3+x^4),x,n+1), x, n), n = 0 .. 30); # _Muniru A Asiru_, Sep 12 2018
%o A038989 (PARI) Vec((1 - x^2 - 2*x^3) / (1 - 2*x - 2*x^2 - 2*x^3 + x^4) + O(x^30)) \\ _Colin Barker_, Jul 16 2017
%o A038989 (GAP) a:=[1,2,5,14];; for n in [5..30] do a[n]:=2*a[n-1]+2*a[n-2]+2*a[n-3]-a[n-4]; od; a; # _Muniru A Asiru_, Sep 12 2018
%K A038989 nonn,easy
%O A038989 0,2
%A A038989 _Colin Mallows_