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 A078004 #14 Sep 08 2022 08:45:08
%S A078004 1,1,0,-3,-7,-8,1,25,56,61,-15,-208,-447,-463,176,1725,3561,3496,
%T A078004 -1855,-14263,-28312,-26243,18401,117600,224641,195681,-175520,
%U A078004 -967043,-1778727,-1447848,1628801,7932025,14054296,10615741,-14809135,-64904048,-110805567,-76993903,132527376
%N A078004 Expansion of (1-x)/(1-2*x+2*x^2+x^3).
%H A078004 G. C. Greubel, <a href="/A078004/b078004.txt">Table of n, a(n) for n = 0..1000</a>
%H A078004 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (2,-2,-1).
%F A078004 G.f.: (1-x)/(1-2*x+2*x^2+x^3).
%F A078004 a(n) = 2*a(n-1) - 2*a(n-2) - a(n-3). - _Wesley Ivan Hurt_, Jul 29 2022
%t A078004 LinearRecurrence[{2,-2,-1}, {1,1,0}, 40] (* or *) CoefficientList[ Series[(1-x)/(1-2*x+2*x^2+x^3), {x,0,40}], x] (* _G. C. Greubel_, Jun 27 2019 *)
%o A078004 (PARI) my(x='x+O('x^40)); Vec((1-x)/(1-2*x+2*x^2+x^3)) \\ _G. C. Greubel_, Jun 27 2019
%o A078004 (Magma) R<x>:=PowerSeriesRing(Integers(), 40); Coefficients(R!( (1-x)/( 1-2*x+2*x^2+x^3) )); // _G. C. Greubel_, Jun 27 2019
%o A078004 (Sage) ((1-x)/(1-2*x+2*x^2+x^3)).series(x, 40).coefficients(x, sparse=False) # _G. C. Greubel_, Jun 27 2019
%o A078004 (GAP) a:=[1,1,0];; for n in [4..40] do a[n]:=2*a[n-1]-2*a[n-2]-a[n-3]; od; a; # _G. C. Greubel_, Jun 27 2019
%K A078004 sign,easy
%O A078004 0,4
%A A078004 _N. J. A. Sloane_, Nov 17 2002