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 A077953 #22 Sep 08 2022 08:45:08
%S A077953 1,1,-1,-1,3,3,-5,-5,11,11,-21,-21,43,43,-85,-85,171,171,-341,-341,
%T A077953 683,683,-1365,-1365,2731,2731,-5461,-5461,10923,10923,-21845,-21845,
%U A077953 43691,43691,-87381,-87381,174763,174763,-349525,-349525,699051,699051,-1398101,-1398101,2796203,2796203,-5592405
%N A077953 Expansion of 1/(1-x+2*x^2-2*x^3).
%C A077953 Essentially the same as A077980.
%H A077953 G. C. Greubel, <a href="/A077953/b077953.txt">Table of n, a(n) for n = 0..1000</a>
%H A077953 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (1, -2, 2).
%F A077953 From _Reinhard Zumkeller_, Oct 07 2008: (Start)
%F A077953 a(n+1) = a(n) - 2*a(n-1) + 2*a(n-2).
%F A077953 a(n) = A077925(floor(n/2)-1) for n>1. (End)
%p A077953 seq(coeff(series(1/(1-x+2*x^2-2*x^3), x, n+1), x, n), n = 0 .. 40); # _G. C. Greubel_, Aug 07 2019
%t A077953 CoefficientList[Series[1/(1-x+2x^2-2x^3),{x,0,50}],x] (* or *) LinearRecurrence[{1,-2,2},{1,1,-1},50] (* _Harvey P. Dale_, Aug 27 2014 *)
%o A077953 (PARI) Vec(1/(1-x+2*x^2-2*x^3)+O(x^50)) \\ _Charles R Greathouse IV_, Sep 25 2012
%o A077953 (Magma) R<x>:=PowerSeriesRing(Integers(), 50); Coefficients(R!( 1/(1-x+2*x^2-2*x^3) )); // _G. C. Greubel_, Aug 07 2019
%o A077953 (Sage) (1/(1-x+2*x^2-2*x^3)).series(x, 50).coefficients(x, sparse=False) # _G. C. Greubel_, Aug 07 2019
%o A077953 (GAP) a:=[1,1,-1];; for n in [4..50] do a[n]:=a[n-1]-2*a[n-2]+2*a[n-3]; od; a; # _G. C. Greubel_, Aug 07 2019
%Y A077953 Cf. A077980.
%Y A077953 Cf. A007420, A077925. - _Reinhard Zumkeller_, Oct 07 2008
%K A077953 sign,easy
%O A077953 0,5
%A A077953 _N. J. A. Sloane_, Nov 17 2002, Jun 17 2007