A126781 - OEIS

This site is supported by donations to The OEIS Foundation.

A126781

a(n) is equal to the number of functions f:{1,2,...,n}->{1,2,...,n} such that Im(f) contains 6 fixed elements.

720, 20160, 514080, 13608000, 385363440, 11760819840, 386860668480, 13682898028800, 518666099711760, 20997894426949440, 904827327153291360, 41367795437773022400, 2000634709955550047280, 102066613831917982920960 (list; graph; refs; listen; history; internal format)

	OFFSET	`6,1`
	LINKS	`Milan Janjic, Enumerative Formulas for Some Functions on Finite Sets`
	FORMULA	`a(n)=n^n-6(n-1)^n+15(n-2)^n-20(n-3)^n+15(n-4)^n-6*(n-5)^n+(n-6)^n, (n=6,7,...)`
	EXAMPLE	`a(7)=20160`
	MAPLE	`a:=n->n^n-6(n-1)^n+15(n-2)^n-20(n-3)^n+15(n-4)^n-6*(n-5)^n+(n-6)^n;`
	CROSSREFS	`Cf. A039621 (Lehmer-Comtet numbers of 2nd kind).` `Sequence in context: A000920 A052779 A037212 * A090008 A003938 A052720` `Adjacent sequences: A126778 A126779 A126780 * A126782 A126783 A126784`
	KEYWORD	`nonn`
	AUTHOR	`Aleksandar M. Janjic and Milan R. Janjic (agnus(AT)blic.net), Feb 18 2007`

Content is available under The OEIS End-User License Agreement .

Last modified February 15 19:09 EST 2012. Contains 205852 sequences.