A327230 - OEIS

A327230

Number of non-isomorphic set-systems covering n vertices with at least one endpoint/leaf.

0, 1, 3, 14, 198

(list; graph; refs; listen; history; text; internal format)

OFFSET

0,3

COMMENTS

A set-system is a finite set of finite nonempty sets. Elements of a set-system are sometimes called edges. A leaf is an edge containing a vertex that does not belong to any other edge, while an endpoint is a vertex belonging to only one edge.

Also covering set-systems with minimum vertex-degree 1.

LINKS

Table of n, a(n) for n=0..4.

EXAMPLE

Non-isomorphic representatives of the a(1) = 1 through a(3) = 14 set-systems:

{{1},{2}} {{1},{2,3}}

{{2},{1,2}} {{1},{2},{3}}

{{1,3},{2,3}}

{{3},{1,2,3}}

{{1},{3},{2,3}}

{{2,3},{1,2,3}}

{{2},{1,3},{2,3}}

{{2},{3},{1,2,3}}

{{3},{1,3},{2,3}}

{{1},{2},{3},{2,3}}

{{3},{2,3},{1,2,3}}

{{2},{3},{1,3},{2,3}}

{{2},{3},{2,3},{1,2,3}}

CROSSREFS

Unlabeled covering set-systems are A055621.

The labeled version is A327229.

The non-covering version is A327335 (partial sums).

Cf. A002494, A245797, A261919, A283877, A327103, A327105, A327197, A327227, A327228.

Sequence in context: A344745 A058388 A362385 * A288555 A288563 A081383

Adjacent sequences: A327227 A327228 A327229 * A327231 A327232 A327233

KEYWORD

nonn,more

AUTHOR

Gus Wiseman, Sep 01 2019

STATUS

approved