A291462 a(n) = (1/2)*A291417(n).

2, 9, 38, 161, 680, 2872, 12128, 51214, 216264, 913228, 3856328, 16284284, 68764352, 290374208, 1226175744, 5177825416, 21864627616, 92328709904, 389880441696, 1646365025296, 6952176889728, 29357258422912, 123968166486528, 523485745182432, 2210545926231680

Offset: 0

Author

Clark Kimberling, Sep 07 2017

Keywords

• nonn
• easy

Links

• Clark Kimberling, Table of n, a(n) for n = 0..1000
• Index entries for linear recurrences with constant coefficients, signature (4, 2, -4, -2)

Crossrefs

Cf. A019590, A291382, A291417.

Programs

Mathematica

z = 60; s = x + x^2; p = 1 - 4 s + 2 s^2;
Drop[CoefficientList[Series[s, {x, 0, z}], x], 1]  (* A019590 *)
u = Drop[CoefficientList[Series[1/p, {x, 0, z}], x], 1]  (* A291417 *)
u / 2  (*A291462)

Formula

G.f.: -(((-1 + x) (1 + x) (2 + x))/(1 - 4 x - 2 x^2 + 4 x^3 + 2 x^4)).

a(n) = 4*a(n-1) + 2*a(n-2) - 4*a(n-3) - 2*a(n-4) for n >= 5.