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A291462
a(n) = (1/2)*A291417(n)..
2
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
0,1
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.
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)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Clark Kimberling, Sep 07 2017
STATUS
approved