A319639 - OEIS

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A319639

Number of antichain covers of n vertices by distinct sets whose dual is also an antichain of distinct sets.

1, 1, 1, 2, 20, 2043

(list; graph; refs; listen; history; text; internal format)

OFFSET

0,4

COMMENTS

The dual of a multiset partition has, for each vertex, one block consisting of the indices (or positions) of the blocks containing that vertex, counted with multiplicity. For example, the dual of {{1,2},{2,2}} is {{1},{1,2,2}}.

LINKS

Table of n, a(n) for n=0..5.

EXAMPLE

The a(1) = 1 through a(3) = 2 antichain covers:

1: {{1}}

2: {{1},{2}}

3: {{1},{2},{3}}

{{1,2},{1,3},{2,3}}

CROSSREFS

Cf. A006126, A007716, A049311, A059201, A283877, A293606, A316980, A316983, A318099, A319558, A319616-A319646, A300913.

Sequence in context: A347608 A244015 A279691 * A134476 A224732 A055746

Adjacent sequences: A319636 A319637 A319638 * A319640 A319641 A319642

KEYWORD

nonn,more

AUTHOR

Gus Wiseman, Sep 25 2018

STATUS

approved