

A326942


Number of unlabeled T_0 sets of subsets of {1..n} that cover all n vertices.


5




OFFSET

0,1


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},{2,3}} is {{1},{1,2},{2}}. The T_0 condition means that the dual is strict (no repeated edges).


LINKS

Table of n, a(n) for n=0..4.


FORMULA

a(n) = 2 * A319637(n).


EXAMPLE

Nonisomorphic representatives of the a(0) = 2 through a(2) = 6 sets of subsets:
{} {{1}} {{1},{2}}
{{}} {{},{1}} {{2},{1,2}}
{{},{1},{2}}
{{},{2},{1,2}}
{{1},{2},{1,2}}
{{},{1},{2},{1,2}}


CROSSREFS

The nonT_0 version is A003181.
The case without empty edges is A319637.
The labeled version is A326939.
The noncovering version is A326949 (partial sums).
Cf. A000371, A003180, A055621, A059201, A316978, A319559, A319564, A326907, A326941, A326943, A326946.
Sequence in context: A137244 A284707 A174589 * A247943 A329571 A270358
Adjacent sequences: A326939 A326940 A326941 * A326943 A326944 A326945


KEYWORD

nonn,more


AUTHOR

Gus Wiseman, Aug 07 2019


STATUS

approved



