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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: 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

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Last modified September 17 08:52 EDT 2024. Contains 375987 sequences. (Running on oeis4.)