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 A078003 #14 Sep 08 2022 08:45:08
%S A078003 1,1,0,0,2,4,4,4,8,16,24,32,48,80,128,192,288,448,704,1088,1664,2560,
%T A078003 3968,6144,9472,14592,22528,34816,53760,82944,128000,197632,305152,
%U A078003 471040,727040,1122304,1732608,2674688,4128768,6373376,9838592,15187968,23445504,36192256
%N A078003 Expansion of (1-x)/(1-2*x+2*x^2-2*x^3).
%H A078003 G. C. Greubel, <a href="/A078003/b078003.txt">Table of n, a(n) for n = 0..1000</a>
%H A078003 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (2,-2,2).
%F A078003 a(n) = A077943(n) - A077943(n-1). - _R. J. Mathar_, Aug 04 2008
%t A078003 LinearRecurrence[{2,-2,2}, {1,1,0}, 50] (* or *) CoefficientList[
%t A078003 Series[(1-x)/(1-2*x+2*x^2-2*x^3), {x,0,50}], x] (* _G. C. Greubel_, Jun 27 2019 *)
%o A078003 (PARI) Vec((1-x)/(1-2*x+2*x^2-2*x^3)+O(x^50)) \\ _Charles R Greathouse IV_, Sep 26 2012
%o A078003 (Magma) R<x>:=PowerSeriesRing(Integers(), 50); Coefficients(R!( (1-x)/( 1-2*x+2*x^2-2*x^3) )); // _G. C. Greubel_, Jun 27 2019
%o A078003 (Sage) ((1-x)/(1-2*x+2*x^2-2*x^3)).series(x, 50).coefficients(x, sparse=False) # _G. C. Greubel_, Jun 27 2019
%o A078003 (GAP) a:=[1,1,0];; for n in [4..50] do a[n]:=2*(a[n-1]-a[n-2]+a[n-3]); od; a; # _G. C. Greubel_, Jun 27 2019
%Y A078003 Cf. A077943.
%K A078003 nonn,easy
%O A078003 0,5
%A A078003 _N. J. A. Sloane_, Nov 17 2002