id:A116218 - OEIS Search Results

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If X_1,...,X_n is a partition of a 2n-set X into 2-blocks (or pairs) then a(n) is equal to the number of permutations f of X such that f(X_i) != X_i for all i=1,...n.

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0, 20, 592, 35088, 3252608, 437765440, 80766186240, 19580003614976, 6038002429456384, 2308538525796209664, 1071858241055770480640, 594103565746026102722560, 387504996819754568329494528, 293818792387460667662661926912, 256273357771747968541309427187712 (list; graph; listen)

	OFFSET	`1,2`
	LINKS	`Milan Janjic, Enumerative Formulas for Some Functions on Finite Sets`
	FORMULA	`a(n)=sum((-2)^ibinomial(n,i)(2n-2i))!,i=0..n).`
	EXAMPLE	`a(5)=3252608`
	MAPLE	`a:=n->sum((-2)^ibinomial(n, i)(2n-2i)!, i=0..n);`
	CROSSREFS	`Sequence in context: A047682 A012568 A027407 this_sequence A035279 A015268 A059420` `Adjacent sequences: A116215 A116216 A116217 this_sequence A116219 A116220 A116221`
	KEYWORD	`nonn`
	AUTHOR	`Milan Janjic (agnus(AT)blic.net), Apr 08 2007, corrected Apr 13 2007`

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Last modified November 18 20:14 EST 2008. Contains 147244 sequences.

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