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 A291384 #6 Sep 04 2017 19:31:00
%S A291384 1,4,14,49,172,604,2120,7442,26124,91704,321912,1130020,3966752,
%T A291384 13924640,48880192,171585992,602324816,2114363648,7422130912,
%U A291384 26054187664,91459003200,321052008000,1127001041280,3956154502688,13887439208896,48749604609664
%N A291384 a(n) = (1/2)*A291383(n).
%H A291384 Clark Kimberling, <a href="/A291384/b291384.txt">Table of n, a(n) for n = 0..1000</a>
%H A291384 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (2, 4, 4, 2)
%F A291384 G.f.: -(((1 + x) (1 + x + x^2))/(-1 + 2 x + 4 x^2 + 4 x^3 + 2 x^4))
%F A291384 a(n) = 2*a(n-1) + 4*a(n-2) + 4*a(n-3) + 2*a(n-4) for n >= 5.
%t A291384 z = 60; s = x + x^2; p = 1 - 2 s - 2 s^2;
%t A291384 Drop[CoefficientList[Series[s, {x, 0, z}], x], 1] (* A019590 *)
%t A291384 u = Drop[CoefficientList[Series[1/p, {x, 0, z}], x], 1] (* A291383 *)
%t A291384 u / 2 (* A291384 *)
%Y A291384 Cf. A019590, A291382, A291383.
%K A291384 nonn,easy
%O A291384 0,2
%A A291384 _Clark Kimberling_, Sep 04 2017