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Search: id:A051578
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| A051578 |
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(2*n+4)!!/4!!, related to A000165 (even double factorials). |
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+0
3
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| 1, 6, 48, 480, 5760, 80640, 1290240, 23224320, 464486400, 10218700800, 245248819200, 6376469299200, 178541140377600, 5356234211328000, 171399494762496000, 5827582821924864000, 209792981589295104000
(list; graph; listen)
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OFFSET
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0,2
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COMMENT
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Row m=4 of the array A(3; m,n) := (2*n+m)!!/m!!, m >= 0, n >= 0.
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LINKS
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INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 521
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FORMULA
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a(n) = (2*n+4)!!/4!!; e.g.f.: 1/(1-2*x)^3.
a(n) ~ 2^(-1/2)*pi^(1/2)*n^(5/2)*2^n*e^-n*n^n*{1 + 37/12*n^-1 + ...}. - Joe Keane (jgk(AT)jgk.org), Nov 23 2001
a(n)=n!*2^(n-3), n>=2 - Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Sep 23 2006
a(n)=2^n*A001710(n+2). - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Feb 22 2008
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MAPLE
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seq(count(Permutation(n))*count(Composition(n))/4, n=2..18); - Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Oct 16 2006
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CROSSREFS
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Cf. A000165, A001147(n+1), A002866(n+1), A051577 (rows m=0..3).
Adjacent sequences: A051575 A051576 A051577 this_sequence A051579 A051580 A051581
Sequence in context: A037184 A085457 A105627 this_sequence A052639 A053506 A055861
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KEYWORD
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easy,nonn
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AUTHOR
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Wolfdieter Lang (wolfdieter.lang(AT)physik.uni-karlsruhe.de)
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