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 A077955 #12 Sep 08 2022 08:45:08
%S A077955 1,1,-1,-4,-3,6,16,7,-31,-61,-6,147,220,-68,-655,-739,639,2772,2233,
%T A077955 -3950,-11188,-5521,20805,43035,6946,-99929,-156856,36056,449697,
%U A077955 534441,-401009,-1919588,-1652011,2588174,7811784,4287447,-13924295,-30310973,-6749830,67796411,111607044,-17235948
%N A077955 Expansion of 1/(1-x+2*x^2+x^3).
%H A077955 G. C. Greubel, <a href="/A077955/b077955.txt">Table of n, a(n) for n = 0..1000</a>
%H A077955 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (1,-2,-1).
%F A077955 a(n) = (-1)^n * A077978(n). - _G. C. Greubel_, Jul 02 2019
%t A077955 LinearRecurrence[{1,-2,-1}, {1,1,-1}, 50] (* or *) CoefficientList[ Series[1/(1-x+2*x^2+x^3), {x,0,50}], x] (* _G. C. Greubel_, Jul 02 2019 *)
%o A077955 (PARI) Vec(1/(1-x+2*x^2+x^3)+O(x^50)) \\ _Charles R Greathouse IV_, Sep 27 2012
%o A077955 (Magma) R<x>:=PowerSeriesRing(Integers(), 50); Coefficients(R!( 1/(1-x+2*x^2+x^3) )); // _G. C. Greubel_, Jul 02 2019
%o A077955 (Sage) (1/(1-x+2*x^2+x^3)).series(x, 50).coefficients(x, sparse=False) # _G. C. Greubel_, Jul 02 2019
%o A077955 (GAP) a:=[1,1,-1];; for n in [4..50] do a[n]:=a[n-1]-2*a[n-2]-a[n-3]; od; a; # _G. C. Greubel_, Jul 02 2019
%Y A077955 Cf. A077978.
%K A077955 sign,easy
%O A077955 0,4
%A A077955 _N. J. A. Sloane_, Nov 17 2002