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A291733
a(n) = (1/4)*A291732(n).
2
1, 3, 9, 26, 72, 195, 520, 1368, 3560, 9184, 23520, 59860, 151536, 381840, 958256, 2396192, 5972736, 14845040, 36801792, 91021056, 224642304, 553347072, 1360598016, 3340024384, 8186748160, 20038426368, 48983457024, 119593531904, 291657627648, 710522702592
OFFSET
0,2
FORMULA
G.f.: -(((1 + x^2) (-1 + x + x^3))/(-1 + 2 x + 2 x^3)^2).
a(n) = 4*a(n-1) - 4*a(n-2) + 4*a(n-3) - 8*a(n-4) - 4*a(n-6) for n >= 7.
MATHEMATICA
z = 60; s = x + x^3; p = (1 - 2 s)^2;
Drop[CoefficientList[Series[s, {x, 0, z}], x], 1] (* A154272 *)
u = Drop[CoefficientList[Series[1/p, {x, 0, z}], x], 1] (* A291732 *)
u / 4 (*A291733)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Clark Kimberling, Sep 11 2017
STATUS
approved