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A090932
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n! / 2^floor(n/2).
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1
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1, 1, 1, 3, 6, 30, 90, 630, 2520, 22680, 113400, 1247400, 7484400, 97297200, 681080400, 10216206000, 81729648000, 1389404016000, 12504636144000, 237588086736000, 2375880867360000, 49893498214560000
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,4
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COMMENTS
| Number of permutations of the n-th row of Pascal's triangle.
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LINKS
| Vincenzo Librandi, Table of n, a(n) for n = 0..200
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FORMULA
| a(n) = binomial(n-1, 2) * a(n-2).
E.g.f.: (1+x)/(1-1/2*x^2).
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EXAMPLE
| a(5) = 5!/2^2 = 120/4 = 30.
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MAPLE
| a:= n-> n!/2^floor(n/2): seq (a(n), n=0..40);
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PROG
| (PARI) a(n)=n!/2^floor(n/2)
(MAGMA) [Factorial(n) / 2^Floor(n/2): n in [0..25]]; // Vincenzo Librandi, May 14 2011
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CROSSREFS
| Cf. A052277, A007019.
The function appears in several expansions: A009775, A046979, A046981, A007415, A007452.
Sequence in context: A136944 A136946 A125521 * A157534 A133799 A088436
Adjacent sequences: A090929 A090930 A090931 * A090933 A090934 A090935
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KEYWORD
| nonn
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AUTHOR
| Jon Perry (perry(AT)globalnet.co.uk), Feb 26 2004
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EXTENSIONS
| Edited by Ralf Stephan (ralf(AT)ark.in-berlin.de), Sep 07 2004
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