A306007 Number of non-isomorphic intersecting antichains of weight n.

1, 1, 1, 1, 2, 2, 6, 6, 14, 22

Offset

0,5

Comments

An intersecting antichain S is a finite set of finite nonempty sets (edges), any two of which have a nonempty intersection, and none of which is a subset of any other. The weight of S 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..9.

Example

Non-isomorphic representatives of the a(8) = 14 set-systems:
{{1,2,3,4,5,6,7,8}}
{{1,7},{2,3,4,5,6,7}}
{{1,2,7},{3,4,5,6,7}}
{{1,5,6},{2,3,4,5,6}}
{{1,2,3,7},{4,5,6,7}}
{{1,2,5,6},{3,4,5,6}}
{{1,3,4,5},{2,3,4,5}}
{{1,2},{1,3,4},{2,3,4}}
{{1,4},{1,5},{2,3,4,5}}
{{1,5},{2,4,5},{3,4,5}}
{{1,6},{2,6},{3,4,5,6}}
{{1,6},{2,3,6},{4,5,6}}
{{2,4},{1,2,5},{3,4,5}}
{{1,5},{2,5},{3,5},{4,5}}

Crossrefs

Cf. A007411, A007716, A034691, A048143, A049311, A116540, A283877, A293606, A293607, A304867, A305999, A305854-A305857, A306005-A306008.

Sequence in context: A056453 A244486 A309800 * A287603 A034422 A140833

Adjacent sequences: A306004 A306005 A306006 * A306008 A306009 A306010

Keyword

nonn,more

Author

Gus Wiseman, Jun 16 2018

Status

approved