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A202689
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a(n) = (2n)! * (n+1)! / 2^(2n).
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1
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1, 1, 9, 270, 18900, 2551500, 589396500, 214540326000, 115851776040000, 88626608670600000, 92614806060777000000, 128364121200236922000000, 230285233433225038068000000, 523898906060586961604700000000, 1485253398681764036149324500000000
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OFFSET
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0,3
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COMMENTS
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a(n) is always an integer since a(n+1)/a(n) = n^3 + 7/2*n^2 + 7/2*n + 1 which is always an integer. [D. S. McNeil, Dec 22 2011]
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LINKS
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FORMULA
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a(n) = (2n)!(n+1)! / 2^(2n).
a(n+1) = a(n)*(n^3 + 7/2*n^2 + 7/2*n + 1).
a(n+1) = a(n)*A002414(n+1) for n >= 0.
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MATHEMATICA
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PROG
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(Magma) [Factorial(2*n)*Factorial(n+1)/2^(2*n): n in [0..15]]; // Vincenzo Librandi, Feb 09 2012
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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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