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A327230 Number of non-isomorphic set-systems covering n vertices with at least one endpoint/leaf. 11
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}}  {{1,2}}      {{1,2,3}}

         {{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: A288559 A132490 A058388 * A288555 A288563 A081383

Adjacent sequences:  A327227 A327228 A327229 * A327231 A327232 A327233

KEYWORD

nonn,more

AUTHOR

Gus Wiseman, Sep 01 2019

STATUS

approved

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Last modified January 24 16:47 EST 2020. Contains 331209 sequences. (Running on oeis4.)