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 A330196 Number of unlabeled set-systems covering n vertices with no endpoints. 1
 1, 0, 1, 20, 1754 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,4 COMMENTS A set-system is a finite set of finite nonempty sets. An endpoint is a vertex appearing only once (degree 1). LINKS Table of n, a(n) for n=0..4. EXAMPLE Non-isomorphic representatives of the a(3) = 20 set-systems: {12}{13}{23} {1}{23}{123} {12}{13}{123} {1}{2}{13}{23} {1}{2}{3}{123} {1}{12}{13}{23} {1}{2}{13}{123} {1}{12}{13}{123} {1}{12}{23}{123} {12}{13}{23}{123} {1}{2}{3}{12}{13} {1}{2}{12}{13}{23} {1}{2}{3}{12}{123} {1}{2}{12}{13}{123} {1}{2}{13}{23}{123} {1}{12}{13}{23}{123} {1}{2}{3}{12}{13}{23} {1}{2}{3}{12}{13}{123} {1}{2}{12}{13}{23}{123} {1}{2}{3}{12}{13}{23}{123} CROSSREFS First differences of the non-covering version A330124. The "multi" version is A302545. Unlabeled set-systems with no endpoints counted by vertices are A317794. Unlabeled set-systems with no endpoints counted by weight are A330054. Unlabeled set-systems counted by vertices are A000612. Unlabeled set-systems counted by weight are A283877. Cf. A007716, A016031, A306005, A317795, A320665, A330052, A330053, A330055. Sequence in context: A177296 A177297 A014606 * A172556 A246619 A222973 Adjacent sequences: A330193 A330194 A330195 * A330197 A330198 A330199 KEYWORD nonn,more AUTHOR Gus Wiseman, Dec 05 2019 STATUS approved

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Last modified September 18 01:15 EDT 2024. Contains 375995 sequences. (Running on oeis4.)