A319783 Number of set systems spanning n vertices with empty intersection whose dual is also a set system with empty intersection.

1, 0, 0, 1, 203, 490572

Offset

0,5

Comments

The dual of a multiset partition has, for each vertex, one part consisting of the indices (or positions) of the parts 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(3) = 1 set system is {{1,2},{1,3},{2,3}}.

Crossrefs

Cf. A007716, A049311, A281116, A283877, A316980, A317752, A317755, A317757.

Cf. A319775, A319778, A319779, A319781.

Sequence in context: A209463 A209525 A145635 * A208306 A208786 A208586

Adjacent sequences: A319780 A319781 A319782 * A319784 A319785 A319786

Keyword

nonn,more

Author

Gus Wiseman, Sep 27 2018

Status

approved