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 A217733 #16 Sep 08 2022 08:46:04
%S A217733 1,2,4,8,15,29,54,103,192,364,680,1285,2405,4536,8501,16014,30040,
%T A217733 56544,106135,199673,374950,705155,1324524,2490416,4678728,8795773,
%U A217733 16526601,31066048,58375577,109724746,206192780,387549816,728303087,1368842229,2572459078,4834829775,9086219464
%N A217733 Expansion of (1+x-x^2)/((1-x)*(1-3*x^2-x^3)).
%H A217733 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (1,3,-2,-1).
%F A217733 G.f.: (1+x-x^2)/(1-x-3*x^2+2*x^3+x^4).
%F A217733 a(n) = sum( A216236(n-k,k), 0<=k<=n ).
%F A217733 a(n) = a(n-1)+3*a(n-2)-2*a(n-3)-a(n-4) for n>=4, a(0)=1, a(1)=2, a(2)=4, a(3)=8.
%F A217733 a(n+1) - a(n) = A065455(n).
%t A217733 CoefficientList[Series[(1 + x - x^2)/((1 - x) (1 - 3 x^2 - x^3)), {x, 0, 40}], x] (* _Bruno Berselli_, Mar 25 2013 *)
%o A217733 (Magma) m:=40; R<x>:=PowerSeriesRing(Integers(), m); Coefficients(R!((1+x-x^2)/((1-x)*(1-3*x^2-x^3)))); // _Bruno Berselli_, Mar 25 2013
%o A217733 (Maxima) makelist(coeff(taylor((1+x-x^2)/((1-x)*(1-3*x^2-x^3)), x, 0, n), x, n), n, 0, 40); /* _Bruno Berselli_, Mar 25 2013 */
%Y A217733 Cf. A065455, A216236.
%K A217733 nonn,easy
%O A217733 0,2
%A A217733 _Philippe Deléham_, Mar 22 2013