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A319189 Number of uniform regular hypergraphs spanning n vertices. 18
1, 1, 2, 3, 10, 29, 3780 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

We define a hypergraph to be any finite set of finite nonempty sets. A hypergraph is uniform if all edges have the same size, and regular if all vertices have the same degree. The span of a hypergraph is the union of its edges.

Also the number of 0-1 matrices with n columns, all distinct rows, no zero columns, equal row-sums, and equal column-sums, up to a permutation of the rows.

LINKS

Table of n, a(n) for n=0..6.

EXAMPLE

The a(4) = 10 edge-sets:

               {{1,2,3,4}}

              {{1,2},{3,4}}

              {{1,3},{2,4}}

              {{1,4},{2,3}}

            {{1},{2},{3},{4}}

        {{1,2},{1,3},{2,4},{3,4}}

        {{1,2},{1,4},{2,3},{3,4}}

        {{1,3},{1,4},{2,3},{2,4}}

    {{1,2,3},{1,2,4},{1,3,4},{2,3,4}}

  {{1,2},{1,3},{1,4},{2,3},{2,4},{3,4}}

Inequivalent representatives of the a(4) = 10 matrices:

  [1 1 1 1]

.

  [1 1 0 0] [1 0 1 0] [1 0 0 1]

  [0 0 1 1] [0 1 0 1] [0 1 1 0]

.

  [1 0 0 0] [1 1 0 0] [1 1 0 0] [1 0 1 0] [1 1 1 0]

  [0 1 0 0] [1 0 1 0] [1 0 0 1] [1 0 0 1] [1 1 0 1]

  [0 0 1 0] [0 1 0 1] [0 1 1 0] [0 1 1 0] [1 0 1 1]

  [0 0 0 1] [0 0 1 1] [0 0 1 1] [0 1 0 1] [0 1 1 1]

.

  [1 1 0 0]

  [1 0 1 0]

  [1 0 0 1]

  [0 1 1 0]

  [0 1 0 1]

  [0 0 1 1]

MATHEMATICA

Table[Sum[SeriesCoefficient[Product[1+Times@@x/@s, {s, Subsets[Range[n], {m}]}], Sequence@@Table[{x[i], 0, k}, {i, n}]], {m, 0, n}, {k, 1, Binomial[n, m]}], {n, 5}]

CROSSREFS

Uniform hypergraphs are counted by A306021. Unlabeled uniform regular multiset partitions are counted by A319056. Regular graphs are A295193. Uniform clutters are A299353.

Cf. A002829, A005176, A007016, A049311, A058891, A101370, A110100, A110101, A321717, A321720.

Sequence in context: A286814 A121909 A153909 * A301971 A319671 A270363

Adjacent sequences:  A319186 A319187 A319188 * A319190 A319191 A319192

KEYWORD

nonn,more

AUTHOR

Gus Wiseman, Dec 17 2018

STATUS

approved

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Last modified May 31 20:23 EDT 2020. Contains 334748 sequences. (Running on oeis4.)