A327425 Number of unlabeled antichains of nonempty sets covering n vertices where every two vertices appear together in some edge (cointersecting).

1, 1, 1, 2, 6, 54

Offset: 0

Author

Gus Wiseman, Sep 11 2019

Keywords

• nonn
• more

Comments

An antichain is a set of sets, none of which is a subset of any other. It is covering if there are no isolated vertices.

Examples

			Non-isomorphic representatives of the a(1) = 1 through a(4) = 6 antichains:
    {1}  {12}  {123}         {1234}
               {12}{13}{23}  {12}{134}{234}
                             {124}{134}{234}
                             {12}{13}{14}{234}
                             {123}{124}{134}{234}
                             {12}{13}{14}{23}{24}{34}
		

Crossrefs

The labeled version is A327020.

Unlabeled covering antichains are A261005.

The weighted version is A327060.

Cf. A006126, A014466, A055621, A293606, A293993, A305844, A307249, A319639, A326704, A327057, A327058, A327358, A327359.