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A174549
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a(n) = (2*n-1)! + (2*n)!.
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3
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3, 30, 840, 45360, 3991680, 518918400, 93405312000, 22230464256000, 6758061133824000, 2554547108585472000, 1175091669949317120000, 646300418472124416000000, 418802671169936621568000000, 315777214062132212662272000000, 274094621805930760590852096000000
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OFFSET
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1,1
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COMMENTS
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Also the number of adjacency matrices for the n-helm graph. - Eric W. Weisstein, May 25 2017
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LINKS
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Eric Weisstein's World of Mathematics, Helm Graph.
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FORMULA
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zeta(2*n+1) = Integral_{u=0..Pi/2} (sin(u)*log(sin(u))^(2*n+1)/(cos(u)^3))*(-2^(2*n+1)/(n*a(n)). Verified for n=1 to 4 on Wolfram Alpha. - Jean-Claude Babois, Oct 28 2014
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MAPLE
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MATHEMATICA
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Table[(2*n - 1)! + (2*n)!, {n, 15}] (* T. D. Noe, Nov 21 2013 *)
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PROG
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(Magma) [Factorial(2*n-1) + Factorial(2*n): n in [1..15]]; // Vincenzo Librandi, Aug 04 2011
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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