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 A078017 #15 Sep 08 2022 08:45:08
%S A078017 1,0,-1,-3,-2,3,11,12,-5,-39,-58,-9,127,252,143,-363,-1010,-933,803,
%T A078017 3756,4819,-543,-12874,-21969,-8009,39708,91655,67965,-103106,-354381,
%U A078017 -387205,173388,1269355,1870377,254246,-4154841,-8149841,-4503492,11956031,32759205,29810158,-26861109
%N A078017 Expansion of (1-x)/(1-x+x^2+2*x^3).
%H A078017 G. C. Greubel, <a href="/A078017/b078017.txt">Table of n, a(n) for n = 0..1000</a>
%H A078017 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (1,-1,-2).
%F A078017 G.f.: (1-x)/(1-x+x^2+2*x^3).
%F A078017 a(n) = A077952(n) - A077952(n-1). - _G. C. Greubel_, Jun 29 2019
%t A078017 LinearRecurrence[{1,-1,-2}, {1,0,-1}, 50] (* or *) CoefficientList[ Series[(1-x)/(1-x+x^2+2*x^3), {x,0,50}], x] (* _G. C. Greubel_, Jun 29 2019 *)
%o A078017 (PARI) Vec((1-x)/(1-x+x^2+2*x^3)+O(x^50)) \\ _Charles R Greathouse IV_, Sep 27 2012
%o A078017 (Magma) R<x>:=PowerSeriesRing(Integers(), 50); Coefficients(R!( (1-x)/(1-x+x^2+2*x^3) )); // _G. C. Greubel_, Jun 29 2019
%o A078017 (Sage) ((1-x)/(1-x+x^2+2*x^3)).series(x, 50).coefficients(x, sparse=False) # _G. C. Greubel_, Jun 29 2019
%o A078017 (GAP) a:=[1,0,-1];; for n in [4..50] do a[n]:=a[n-1]-a[n-2]-2*a[n-3]; od; a; # _G. C. Greubel_, Jun 29 2019
%Y A078017 Cf. A077952.
%K A078017 sign,easy
%O A078017 0,4
%A A078017 _N. J. A. Sloane_, Nov 17 2002