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A081125
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n!/floor(n/2)!.
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4
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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; refs; listen; history; internal format)
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OFFSET
| 0,3
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REFERENCES
| Peter Luschny, "Divide, swing and conquer the factorial and the lcm{1,2,...,n}", preprint, April 2008. [From Peter Luschny, Aug 07 2009]
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LINKS
| Vincenzo Librandi, Table of n, a(n) for n = 0..400
Index to divisibility sequences
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FORMULA
| a(n) = n!/floor(n/2)!
E.g.f.: (1+x)*exp(x^2). - Vladeta Jovovic (vladeta(AT)eunet.rs), Sep 24 2003
Contribution from Peter Luschny, 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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PROG
| (MAGMA) [Factorial(n)/(Factorial(Floor(n/2))): n in [0..30]]; // Vincenzo Librandi, Sep 13 2011
(PARI) a(n)=n!/(n\2)! \\ Charles R Greathouse IV, Sep 13 2011
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CROSSREFS
| Cf. A081123, A004526.
Sequence in context: A191836 A072486 A096123 * A138570 A161887 A139315
Adjacent sequences: A081122 A081123 A081124 * A081126 A081127 A081128
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KEYWORD
| nonn,easy
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AUTHOR
| Paul Barry (pbarry(AT)wit.ie), Mar 07 2003
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