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 A078011 #15 Sep 08 2022 08:45:08
%S A078011 1,0,1,-1,0,-3,-1,-4,1,-1,8,5,15,4,9,-17,-16,-51,-33,-52,17,31,152,
%T A078011 149,239,84,25,-369,-512,-931,-705,-612,545,1343,3112,3365,3791,932,
%U A078011 -2007,-8657,-12528,-17171,-12385,-4500,17457,37727,64184,66997,55727,-5644,-83911,-201009,-273632,-306819
%N A078011 Expansion of (1-x)/(1-x-x^2+2*x^3).
%H A078011 G. C. Greubel, <a href="/A078011/b078011.txt">Table of n, a(n) for n = 0..1000</a>
%H A078011 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (1,1,-2).
%F A078011 a(0)=1, a(1)=0, a(2)=1, a(n) = a(n-1) + a(n-2) - 2*a(n-3). - _Harvey P. Dale_, May 04 2013
%F A078011 a(n) = A077948(n) - A077948(n-1). - _R. J. Mathar_, Nov 07 2015
%t A078011 CoefficientList[Series[(1-x)/(1-x-x^2+2x^3),{x,0,60}],x] (* or *) LinearRecurrence[ {1,1,-2},{1,0,1},60] (* _Harvey P. Dale_, May 04 2013 *)
%o A078011 (PARI) my(x='x+O('x^60)); Vec((1-x)/(1-x-x^2+2*x^3)) \\ _G. C. Greubel_, Jun 28 2019
%o A078011 (Magma) R<x>:=PowerSeriesRing(Integers(), 60); Coefficients(R!( (1-x)/(1-x-x^2+2*x^3) )); // _G. C. Greubel_, Jun 28 2019
%o A078011 (Sage) ((1-x)/(1-x-x^2+2*x^3)).series(x, 60).coefficients(x, sparse=False) # _G. C. Greubel_, Jun 28 2019
%o A078011 (GAP) a:=[1,0,1];; for n in [4..60] do a[n]:=a[n-1]+a[n-2]-2*a[n-3]; od; a; # _G. C. Greubel_, Jun 28 2019
%Y A078011 Cf. A077948.
%K A078011 sign,easy
%O A078011 0,6
%A A078011 _N. J. A. Sloane_, Nov 17 2002