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A290905
a(n) = (1/2)*A290904(n).
3
0, 1, 4, 12, 36, 111, 344, 1064, 3288, 10161, 31404, 97060, 299980, 927135, 2865456, 8856144, 27371312, 84595361, 261455316, 808068924, 2497464564, 7718808463, 23856195976, 73731339384, 227878342920, 704293989585, 2176731748220, 6727533066836, 20792502889884
OFFSET
0,3
FORMULA
G.f.: x/(1 - 4 x + 4 x^2 - 4 x^3 + x^4).
a(n) = 4*a(n-1) - 4*a(n-2) + 4*a(n-3) - a(n-4).
a(n) = (1/2)*A290904(n) for n >= 0.
MATHEMATICA
z = 60; s = x/(1 - x)^2; p = 1 - 2 s^2;
Drop[CoefficientList[Series[s, {x, 0, z}], x], 1] (* A000027 *)
u = Drop[CoefficientList[Series[1/p, {x, 0, z}], x], 1] (* A290904 *)
u/2 (* A290905 *)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Clark Kimberling, Aug 17 2017
STATUS
approved