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 A290905 #8 Aug 18 2017 18:49:59
%S A290905 0,1,4,12,36,111,344,1064,3288,10161,31404,97060,299980,927135,
%T A290905 2865456,8856144,27371312,84595361,261455316,808068924,2497464564,
%U A290905 7718808463,23856195976,73731339384,227878342920,704293989585,2176731748220,6727533066836,20792502889884
%N A290905 a(n) = (1/2)*A290904(n).
%H A290905 Clark Kimberling, <a href="/A290905/b290905.txt">Table of n, a(n) for n = 0..1000</a>
%H A290905 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (4, -4, 4, -1)
%F A290905 G.f.: x/(1 - 4 x + 4 x^2 - 4 x^3 + x^4).
%F A290905 a(n) = 4*a(n-1) - 4*a(n-2) + 4*a(n-3) - a(n-4).
%F A290905 a(n) = (1/2)*A290904(n) for n >= 0.
%t A290905 z = 60; s = x/(1 - x)^2; p = 1 - 2 s^2;
%t A290905 Drop[CoefficientList[Series[s, {x, 0, z}], x], 1] (* A000027 *)
%t A290905 u = Drop[CoefficientList[Series[1/p, {x, 0, z}], x], 1] (* A290904 *)
%t A290905 u/2 (* A290905 *)
%Y A290905 Cf. A000027, A290890, A290904.
%K A290905 nonn,easy
%O A290905 0,3
%A A290905 _Clark Kimberling_, Aug 17 2017