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A165434 Number of tri-coverings of a set. 8
1, 1, 4, 39, 862, 35775, 2406208, 238773109, 32867762616, 6009498859909, 1412846181645855, 416415343791239162, 150747204270574506888, 65905473934553360340713, 34305461329980340135062217, 21003556204331356488142290707, 14967168378184553824642693791437 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

LINKS

Andrew Howroyd, Table of n, a(n) for n = 0..100

E. A. Bender, Partitions of multisets, Discrete Mathematics 9 (1974) 301-312.

J. S. Devitt and D. M. Jackson, The enumeration of covers of a finite set, J. London Math. Soc.(2) 25 (1982), 1-6.

Doron Zeilberger, In How Many Ways Can You Reassemble Several Russian Dolls?, has links to more terms and related sequences

Doron Zeilberger, In How Many Ways Can You Reassemble Several Russian Dolls?, arXiv:0909.3453 [math.CO], 2009.

Doron Zeilberger, BABUSHKAS

EXAMPLE

For n=2, a(2)=4, since if you have two sets of identical triples the A-brothers and the B-sisters, and you want to arrange them into a multiset of nonempty sets, where no one is allowed to cohabitate with his or her sibling, the following are possible 1.{{AB},{AB},{AB}} 2.{{AB},{AB},{A},{B}} 3.{{AB},{A},{A},{B},{B}} 4.{{A},{A},{A},{B},{B},{B}}.

MAPLE

Do SeqBrn(3, n); in the Maple package BABUSHKAS (see links) where n+1 is the number of desired terms.

CROSSREFS

Row 3 of A188392.

Cf. A000110 (unicoverings), A020554 (bicoverings).

Sequence in context: A299426 A188418 A136653 * A086217 A203197 A094156

Adjacent sequences:  A165431 A165432 A165433 * A165435 A165436 A165437

KEYWORD

nonn

AUTHOR

Doron Zeilberger, Sep 18 2009

EXTENSIONS

Edited by Charles R Greathouse IV, Oct 28 2009

STATUS

approved

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Last modified December 1 21:02 EST 2020. Contains 338858 sequences. (Running on oeis4.)