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 A291733 #4 Sep 11 2017 20:04:56
%S A291733 1,3,9,26,72,195,520,1368,3560,9184,23520,59860,151536,381840,958256,
%T A291733 2396192,5972736,14845040,36801792,91021056,224642304,553347072,
%U A291733 1360598016,3340024384,8186748160,20038426368,48983457024,119593531904,291657627648,710522702592
%N A291733 a(n) = (1/4)*A291732(n).
%H A291733 Clark Kimberling, <a href="/A291733/b291733.txt">Table of n, a(n) for n = 0..1000</a>
%H A291733 <a href="/index/Rec#order_06">Index entries for linear recurrences with constant coefficients</a>, signature (4, -4, 4, -8, 0, -4)
%F A291733 G.f.: -(((1 + x^2) (-1 + x + x^3))/(-1 + 2 x + 2 x^3)^2).
%F A291733 a(n) = 4*a(n-1) - 4*a(n-2) + 4*a(n-3) - 8*a(n-4) - 4*a(n-6) for n >= 7.
%t A291733 z = 60; s = x + x^3; p = (1 - 2 s)^2;
%t A291733 Drop[CoefficientList[Series[s, {x, 0, z}], x], 1] (* A154272 *)
%t A291733 u = Drop[CoefficientList[Series[1/p, {x, 0, z}], x], 1] (* A291732 *)
%t A291733 u / 4 (*A291733)
%Y A291733 Cf. A154272, A291728, A291732.
%K A291733 nonn,easy
%O A291733 0,2
%A A291733 _Clark Kimberling_, Sep 11 2017