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A254529 a(n) = n! * (number of mapping patterns on n). 1
1, 1, 6, 42, 456, 5640, 93600, 1728720, 38344320, 948931200, 26555558400, 817935148800, 27735629644800, 1020596255078400, 40642432179148800, 1737890081351424000, 79498734605402112000, 3871319396080840704000, 200017645344178421760000, 10925549584125028909056000 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

a(n) is the number of ordered pairs (p, f) such that p f = f p, where p is a permutation and f is an endofunction.

LINKS

Table of n, a(n) for n=0..19.

Math Overflow, What is the probability two random maps on n symbols commute?, 2013.

FORMULA

a(n) = n! * A001372(n). - Joerg Arndt, Feb 01 2015

CROSSREFS

Cf. A001372, A053529, A181162.

Sequence in context: A245248 A197712 A306173 * A098461 A284161 A034662

Adjacent sequences:  A254526 A254527 A254528 * A254530 A254531 A254532

KEYWORD

nonn,easy

AUTHOR

Martin Fuller, Feb 01 2015

STATUS

approved

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Last modified February 23 16:28 EST 2020. Contains 332179 sequences. (Running on oeis4.)