The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A319190 Number of regular hypergraphs spanning n vertices. 20
 1, 1, 3, 19, 879, 5280907, 1069418570520767 (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 regular if all vertices have the same degree. The span of a hypergraph is the union of its edges. LINKS EXAMPLE The a(3) = 19 regular hypergraphs:                  {{1,2,3}}                 {{1},{2,3}}                 {{2},{1,3}}                 {{3},{1,2}}                {{1},{2},{3}}             {{1},{2,3},{1,2,3}}             {{2},{1,3},{1,2,3}}             {{3},{1,2},{1,2,3}}             {{1,2},{1,3},{2,3}}            {{1},{2},{3},{1,2,3}}            {{1},{2},{1,3},{2,3}}            {{1},{3},{1,2},{2,3}}            {{2},{3},{1,2},{1,3}}         {{1,2},{1,3},{2,3},{1,2,3}}        {{1},{2},{1,3},{2,3},{1,2,3}}        {{1},{3},{1,2},{2,3},{1,2,3}}        {{2},{3},{1,2},{1,3},{1,2,3}}       {{1},{2},{3},{1,2},{1,3},{2,3}}   {{1},{2},{3},{1,2},{1,3},{2,3},{1,2,3}} MATHEMATICA Table[Sum[SeriesCoefficient[Product[1+Times@@x/@s, {s, Subsets[Range[n], {1, n}]}], Sequence@@Table[{x[i], 0, k}, {i, n}]], {k, 1, 2^n}], {n, 5}] CROSSREFS Column sums of A188445. Cf. A002829, A005176, A049311, A058891, A110100, A110101, A116539, A283877, A295193, A306017, A319189. Sequence in context: A107706 A330040 A168591 * A014015 A114301 A258669 Adjacent sequences:  A319187 A319188 A319189 * A319191 A319192 A319193 KEYWORD nonn,more AUTHOR Gus Wiseman, Dec 17 2018 EXTENSIONS a(6) from Andrew Howroyd, Mar 12 2020 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified October 25 03:06 EDT 2020. Contains 338011 sequences. (Running on oeis4.)