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A258213 Number of permutations of {1,2,3,...,n} such that no even numbers are adjacent. 1
1, 1, 2, 6, 12, 72, 144, 1440, 2880, 43200, 86400, 1814400, 3628800, 101606400, 203212800, 7315660800, 14631321600, 658409472000, 1316818944000, 72425041920000, 144850083840000, 9560105533440000, 19120211066880000, 1491376463216640000, 2982752926433280000 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

LINKS

Table of n, a(n) for n=0..24.

FORMULA

a(n) = factorial(ceiling(n/2))*fallfac(ceiling(n/2)+1, floor(n/2)), with fallfac = A008279.

a(2n) = A010790(n), a(2n-1) = A010790(n)/2.

CROSSREFS

Cf. A008279, A010790.

Sequence in context: A090747 A287142 A076220 * A178846 A173843 A107763

Adjacent sequences:  A258210 A258211 A258212 * A258214 A258215 A258216

KEYWORD

nonn

AUTHOR

Ran Pan, May 23 2015

STATUS

approved

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Last modified September 26 06:54 EDT 2017. Contains 292502 sequences.