id:A027616 - OEIS Search Results

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Number of permutations of n elements containing a 2-cycle.

+0
3

0, 0, 1, 3, 9, 45, 285, 1995, 15855, 142695, 1427895, 15706845, 188471745, 2450132685, 34301992725, 514529890875 (list; graph; listen)

	OFFSET	`0,4`
	FORMULA	`n! * { 1 - sum[ k=0..floor(n/2) ] (-1)^k / (2^k * k!) }.` `a(n) + A000266(n) = n!. - Yuval Dekel (dekelyuval(AT)hotmail.com), Nov 09 2003`
	CROSSREFS	`Adjacent sequences: A027613 A027614 A027615 this_sequence A027617 A027618 A027619` `Sequence in context: A138315 A038059 A004990 this_sequence A013492 A106341 A065407`
	KEYWORD	`nonn`
	AUTHOR	`Joe Keane (jgk(AT)jgk.org)`

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Last modified October 11 13:47 EDT 2008. Contains 144830 sequences.