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 A077913 #17 Sep 08 2022 08:45:07
%S A077913 1,0,-1,1,2,-2,-2,5,2,-9,1,16,-8,-24,25,32,-57,-31,114,6,-202,77,322,
%T A077913 -273,-447,672,496,-1392,-271,2560,-625,-4223,2914,6158,-7762,-7467,
%U A077913 16834,5863,-32063,3504,54760,-29704,-83319,87968,108375,-200991,-103726,397334,11110,-702051,282498,1110495
%N A077913 Expansion of 1/((1-x)*(1+x+2*x^2+x^3)).
%H A077913 G. C. Greubel, <a href="/A077913/b077913.txt">Table of n, a(n) for n = 0..1000</a>
%H A077913 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (0,-1,1,1).
%F A077913 G.f.: 1-x^2/(U(0)+x^2) where U(k)= 1 + (1+x)*x/( 1 - (1+x)*x/((1+x)*x + 1/U(k+1))) ; (continued fraction, 2-step). - _Sergei N. Gladkovskii_, Oct 24 2012
%F A077913 5*a(n) = 1 + 4*A077979(n) + 3*A077979(n-1) + A077979(n-2). - _R. J. Mathar_, Jul 10 2013
%t A077913 LinearRecurrence[{0,-1,1,1}, {1,0,-1,1}, 60] (* or *) CoefficientList[ Series[1/((1-x)*(1+x+2*x^2+x^3)), {x,0,60}], x] (* _G. C. Greubel_, Jul 02 2019 *)
%o A077913 (PARI) my(x='x+O('x^60)); Vec(1/((1-x)*(1+x+2*x^2+x^3))) \\ _G. C. Greubel_, Jul 02 2019
%o A077913 (Magma) R<x>:=PowerSeriesRing(Integers(), 60); Coefficients(R!( 1/((1-x)*(1+x+2*x^2+x^3)) )); // _G. C. Greubel_, Jul 02 2019
%o A077913 (Sage) (1/((1-x)*(1+x+2*x^2+x^3))).series(x, 60).coefficients(x, sparse=False) # _G. C. Greubel_, Jul 02 2019
%o A077913 (GAP) a:=[1,0,-1,1];; for n in [5..60] do a[n]:=-a[n-2]+a[n-3]+a[n-4]; od; a; # _G. C. Greubel_, Jul 02 2019
%K A077913 sign,easy
%O A077913 0,5
%A A077913 _N. J. A. Sloane_, Nov 17 2002