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A237884
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a(n) = (n!*m)/(m!*(m+1)!) where m = floor(n/2).
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1
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0, 0, 1, 3, 4, 20, 15, 105, 56, 504, 210, 2310, 792, 10296, 3003, 45045, 11440, 194480, 43758, 831402, 167960, 3527160, 646646, 14872858, 2496144, 62403600, 9657700, 260757900, 37442160, 1085822640, 145422675, 4508102925, 565722720, 18668849760, 2203961430
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OFFSET
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0,4
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LINKS
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FORMULA
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a(n) = n^(n mod 2)*binomial(2*floor(n/2), floor(n/2)-1).
a(n) = A162246(n, n+2) = n!/((n-ceiling((n+2)/2))!*floor((n+2)/2)!)) if n > 1, otherwise 0.
a(n) = A056040(n)*floor(n/2)/(floor(n/2)+1).
G.f.: -((p - 1 - x*(p - 1 + 2*x*(2*p - 3 + x*(3 + 4*x - 2*p))))/(2*x^2*p^3)), where p=sqrt(1-4*x^2). - Benedict W. J. Irwin, Aug 15 2016
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MAPLE
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A237884 := proc(n) m := iquo(n, 2); (n!*m)/(m!*(m+1)!) end;
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MATHEMATICA
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CoefficientList[Series[-((-1 + Sqrt[1 - 4 x^2] -x (-1 + Sqrt[1 - 4 x^2] +
2 x (-3 + 2 Sqrt[1 - 4 x^2] +x (3 + 4 x - 2 Sqrt[1 - 4 x^2]))))/
Table[(n! #)/(#! (# + 1)!) &@ Floor[n/2], {n, 0, 34}] (* Michael De Vlieger, Aug 15 2016 *)
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PROG
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(Sage)
r, s, n = 1, 0, 0
while True:
yield s
n += 1
r *= 4/n if is_even(n) else n
s = r * (n//2)/(n//2+1)
a = A237884(); [next(a) for i in range(35)]
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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