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A291406
a(n) = (1/2)A291405(n).
2
0, 1, 2, 4, 12, 26, 60, 145, 336, 796, 1880, 4412, 10400, 24488, 57648, 135794, 319744, 752908, 1773016, 4175032, 9831472, 23151400, 54516976, 128377380, 302304640, 711870368, 1676321856, 3947423264, 9295440640, 21889019712, 51544533376, 121377706184
OFFSET
0,3
LINKS
FORMULA
G.f.: -((x (1 + x)^2 (1 + x^2 + 2 x^3 + x^4))/(-1 + 2 x^2 + 4 x^3 + 4 x^4 + 8 x^5 + 12 x^6 + 8 x^7 + 2 x^8)).
a(n) = 2*a(n-2) + 4*a(n-3) + 4*a(n-4) + 5*a(n-5) + 12*a(n-6) + 8*a(n-7) + 2*a(n-8) for n >= 9.
MATHEMATICA
z = 60; s = x + x^2; p = 1 - 2 s^2 - 2 s^4;
Drop[CoefficientList[Series[s, {x, 0, z}], x], 1] (* A019590 *)
u = Drop[CoefficientList[Series[1/p, {x, 0, z}], x], 1] (* A291405 *)
u / 2 (* A291406 *)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Clark Kimberling, Sep 07 2017
STATUS
approved