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Search: id:A081125
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| 1, 1, 2, 6, 12, 60, 120, 840, 1680, 15120, 30240, 332640, 665280, 8648640, 17297280, 259459200, 518918400, 8821612800, 17643225600, 335221286400, 670442572800, 14079294028800, 28158588057600, 647647525324800, 1295295050649600
(list; graph; listen)
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OFFSET
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0,3
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COMMENT
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Contribution from Peter Luschny (peter(AT)luschny.de), Aug 07 2009: (Start)
a(n) = sqrt(n! n$) where n$ denotes the swinging factorial (A056040).
a(n) = 2^n Gamma((n+1+(n mod 2))/2)/sqrt(Pi). (End)
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REFERENCES
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Peter Luschny, "Divide, swing and conquer the factorial and the lcm{1,2,...,n}", preprint, April 2008. [From Peter Luschny (peter(AT)luschny.de), Aug 07 2009]
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FORMULA
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a(n) =n!/floor(n/2)!
E.g.f.: (1+x)*exp(x^2). - Vladeta Jovovic (vladeta(AT)eunet.rs), Sep 24 2003
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CROSSREFS
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Cf. A081123, A004526.
Sequence in context: A135060 A072486 A096123 this_sequence A138570 A161887 A139315
Adjacent sequences: A081122 A081123 A081124 this_sequence A081126 A081127 A081128
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KEYWORD
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easy,nonn
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AUTHOR
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Paul Barry (pbarry(AT)wit.ie), Mar 07 2003
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