A305856 Number of unlabeled intersecting set-systems on up to n vertices.

1, 2, 4, 14, 124, 14992, 1289845584

Offset: 0

Author

Gus Wiseman, Jun 11 2018

Keywords

• nonn
• more

Comments

An intersecting set-system is a finite set of finite nonempty sets (edges), any two of which have a nonempty intersection.

Examples

			Non-isomorphic representatives of the a(3) = 14 intersecting set-systems:
  {}
  {{1}}
  {{1,2}}
  {{1,2,3}}
  {{2},{1,2}}
  {{3},{1,2,3}}
  {{1,3},{2,3}}
  {{2,3},{1,2,3}}
  {{3},{1,3},{2,3}}
  {{3},{2,3},{1,2,3}}
  {{1,2},{1,3},{2,3}}
  {{1,3},{2,3},{1,2,3}}
  {{3},{1,3},{2,3},{1,2,3}}
  {{1,2},{1,3},{2,3},{1,2,3}}
		

Crossrefs

Cf. A001206, A006126, A051185, A261006, A283877, A304982, A304996, A304998, A305843, A305844, A305854-A305857.

Extensions

a(5) from Andrew Howroyd, Aug 12 2019

a(6) from Bert Dobbelaere, Apr 28 2025