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A091535
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First column (k=2) of array A091534 ((5,2)-Stirling2).
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3
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1, 20, 1120, 123200, 22422400, 6098892800, 2317579264000, 1172695107584000, 762251819929600000, 618948477782835200000, 613996889960572518400000, 730656299053081296896000000, 1027302756468632303435776000000, 1684776520608556977634672640000000
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OFFSET
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1,2
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COMMENTS
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The scaled sequence (2/(3n-1)!!!)*a(n) = (3*n-2)!!! = A007559(n), n>=1.
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LINKS
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FORMULA
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a(n) = (3*n-1)!/(2!*3^(n-(2-1))*(n-1)!) = ((3*n-1)!/2)/A032031(n-1).
E.g.f.: (hypergeom([1/3, 2/3, 1], [], 9*x)-1)/2.
a(n) = 9^n*Gamma(n+1/3)*Gamma(n+2/3)*sqrt(3)/(4*Pi). - Peter Luschny, Sep 17 2014
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MAPLE
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a := n -> 9^n*GAMMA(n+1/3)*GAMMA(n+2/3)*sqrt(3)/(4*Pi);
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CROSSREFS
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Third column of array A091752 ((-1, 2)-Stirling2).
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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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