A326939 - OEIS

A326939

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

2, 2, 8, 192, 63384, 4294003272, 18446743983526539408, 340282366920938462946865774750753349904, 115792089237316195423570985008687907841019819456486779364848020385134373080448

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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..8.

FORMULA

a(n) = 2 * A059201(n).

Inverse binomial transform of A326941.

EXAMPLE

The a(0) = 2 through a(2) = 8 sets of subsets:

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

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

{{2},{1,2}}

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

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

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

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

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

MATHEMATICA

dual[eds_]:=Table[First/@Position[eds, x], {x, Union@@eds}];

Table[Length[Select[Subsets[Subsets[Range[n]]], Union@@#==Range[n]&&UnsameQ@@dual[#]&]], {n, 0, 3}]

CROSSREFS

The non-T_0 version is A000371.

The case without empty edges is A059201.

The non-covering version is A326941.

The unlabeled version is A326942.

The case closed under intersection is A326943.

Cf. A003180, A003181, A003465, A316978, A319564, A319637, A326940, A326947.

Sequence in context: A270316 A069561 A180370 * A341303 A011148 A365307

Adjacent sequences: A326936 A326937 A326938 * A326940 A326941 A326942

KEYWORD

nonn

AUTHOR

Gus Wiseman, Aug 07 2019

STATUS

approved