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 A117666 #10 Sep 08 2022 08:45:24
%S A117666 1,-2,-3,2,3,2,3,0,-1,4,5,4,5,2,1,6,7,6,7,4,3,8,9,8,9,6,5,10,11,10,11,
%T A117666 8,7,12,13,12,13,10,9,14,15,14,15,12,11,16,17,16,17,14,13,18,19,18,19,
%U A117666 16,15,20,21,20,21,18,17,22,23,22,23,20,19,24,25,24,25,22,21,26,27,26,27,24,23,28,29,28,29,26,25
%N A117666 Expansion of (1-3*x+x^2)*(1-x-x^2)/((1+x+x^2)*(1-x+x^2)*(1-x)^2).
%H A117666 Colin Barker, <a href="/A117666/b117666.txt">Table of n, a(n) for n = 0..1000</a>
%H A117666 <a href="/index/Rec#order_06">Index entries for linear recurrences with constant coefficients</a>, signature (2,-2,2,-2,2,-1).
%F A117666 a(n) = 2*a(n-1) - 2*a(n-2) + 2*a(n-3) - 2*a(n-4) + 2*a(n-5) - a(n-6) for n>5. - _Colin Barker_, May 18 2019
%t A117666 CoefficientList[Series[(1-3*x+x^2)*(1-x-x^2)/((1+x^2+x^4)*(1-x)^2), {x, 0, 100}], x] (* _G. C. Greubel_, Jul 13 2019 *)
%o A117666 (PARI) Vec((1-3*x+x^2)*(1-x-x^2)/((1-x)^2*(1+x^2+x^4)) + O(x^100)) \\ _Colin Barker_, May 18 2019
%o A117666 (Magma) R<x>:=PowerSeriesRing(Integers(), 100); Coefficients(R!( (1-3*x+x^2)*(1-x-x^2)/((1+x^2+x^4)*(1-x)^2) )); // _G. C. Greubel_, Jul 13 2019
%o A117666 (Sage) ((1-3*x+x^2)*(1-x-x^2)/((1+x^2+x^4)*(1-x)^2)).series(x, 100).coefficients(x, sparse=False) # _G. C. Greubel_, Jul 13 2019
%o A117666 (GAP) a:=[1,-2,-3,2,3,2];; for n in [7..100] do a[n]:=2*a[n-1] -2*a[n-2] +2*a[n-3] -2*a[n-4] +2*a[n-5] -a[n-6]; od; a; # _G. C. Greubel_, Jul 13 2019
%Y A117666 Cf. A104161, A001595.
%K A117666 easy,sign
%O A117666 0,2
%A A117666 _Creighton Dement_, Apr 11 2006