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 A091919 #13 Sep 08 2022 08:45:13
%S A091919 1,2,6,12,27,54,112,224,453,906,1818,3636,7279,14558,29124,58248,
%T A091919 116505,233010,466030,932060,1864131,3728262,7456536,14913072,
%U A091919 29826157,59652314,119304642,238609284,477218583,954437166,1908874348,3817748696
%N A091919 Expansion of 1/((1-2*x)*(1-x^2)^2).
%H A091919 G. C. Greubel, <a href="/A091919/b091919.txt">Table of n, a(n) for n = 0..1000</a>
%H A091919 <a href="/index/Rec#order_05">Index entries for linear recurrences with constant coefficients</a>, signature (2,2,-4,-1,2).
%F A091919 a(n) = 2^(n+4)/9 + (3*n+8)*(-1)^n/36 - (n+4)/4.
%F A091919 a(n) = Sum_{k=0..floor(n/2)} A000975(n-2*k+1). - _Paul Barry_, Jan 18 2009
%t A091919 CoefficientList[Series[1/((1 - 2*x)*(1 - x^2)^2), {x, 0, 50}], x] (* _G. C. Greubel_, Oct 11 2017 *)
%t A091919 LinearRecurrence[{2,2,-4,-1,2},{1,2,6,12,27},40] (* _Harvey P. Dale_, Oct 23 2019 *)
%o A091919 (PARI) for(n=0, 50, print1(2^(n+4)/9 + (3*n+8)*(-1)^n/36 - (n+4)/4, ", ")) \\ _G. C. Greubel_, Oct 11 2017
%o A091919 (Magma) [2^(n+4)/9 + (3*n+8)*(-1)^n/36 - (n+4)/4: n in [0..30]]; // _G. C. Greubel_, Oct 11 2017
%K A091919 easy,nonn
%O A091919 0,2
%A A091919 _Paul Barry_, Feb 13 2004