A306008 Number of non-isomorphic intersecting set-systems of weight n with no singletons.

1, 0, 1, 1, 2, 3, 7, 10, 21, 39, 78

Offset

0,5

Comments

An intersecting set-system is a finite set of finite nonempty sets (edges), any two of which have a nonempty intersection. The weight of a set-system is the sum of cardinalities of its elements. Weight is generally not the same as number of vertices.

Links

Table of n, a(n) for n=0..10.

Example

Non-isomorphic representatives of the a(6) = 7 set-systems:
{{1,2,3,4,5,6}}
{{1,5},{2,3,4,5}}
{{3,4},{1,2,3,4}}
{{1,2,5},{3,4,5}}
{{1,3,4},{2,3,4}}
{{1,2},{1,3},{2,3}}
{{1,4},{2,4},{3,4}}

Crossrefs

Cf. A007716, A034691, A048143, A049311, A116540, A283877, A293606, A293607, A304867, A305999, A305854-A305857, A306005-A306007.

Sequence in context: A336414 A095010 A295723 * A291241 A318406 A365967

Adjacent sequences: A306005 A306006 A306007 * A306009 A306010 A306011

Keyword

nonn,more

Author

Gus Wiseman, Jun 16 2018

Status

approved