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 A077975 #18 Sep 08 2022 08:45:08
%S A077975 1,-1,0,3,-5,2,9,-21,16,23,-81,90,37,-289,432,-69,-941,1874,-1071,
%T A077975 -2685,7504,-6961,-5913,27882,-35891,-3817,95472,-163437,60331,294050,
%U A077975 -681255,507867,761488,-2631865,2886111,1268730,-9418571,13922063,-1966032,-30793173,60603331,-33742222,-88447455
%N A077975 Expansion of 1/(1+x+x^2-2*x^3).
%H A077975 G. C. Greubel, <a href="/A077975/b077975.txt">Table of n, a(n) for n = 0..1000</a>
%H A077975 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (-1,-1,2).
%F A077975 Recurrence: a(n) = 2a(n-3) - a(n-2) - a(n-1), starting 1,-1,0. - _Ralf Stephan_, Aug 18 2013
%t A077975 CoefficientList[Series[1/(1+x+x^2-2x^3),{x,0,50}],x] (* or *) LinearRecurrence[ {-1,-1,2},{1,-1,0},50] (* _Harvey P. Dale_, Jul 20 2015 *)
%o A077975 (PARI) Vec(1/(1+x+x^2-2*x^3)+O(x^50)) \\ _Charles R Greathouse IV_, Sep 26 2012
%o A077975 (Magma) R<x>:=PowerSeriesRing(Integers(), 50); Coefficients(R!( 1/(1+x+x^2-2*x^3) )); // _G. C. Greubel_, Jun 25 2019
%o A077975 (Sage) (1/(1+x+x^2-2*x^3)).series(x, 50).coefficients(x, sparse=False) # _G. C. Greubel_, Jun 25 2019
%o A077975 (GAP) a:=[1,-1,0];; for n in [4..50] do a[n]:=-a[n-1]-a[n-2]+2*a[n-3]; od; a; # _G. C. Greubel_, Jun 25 2019
%K A077975 sign,easy
%O A077975 0,4
%A A077975 _N. J. A. Sloane_, Nov 17 2002