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 A305856 Number of unlabeled intersecting set-systems on up to n vertices. 3
 1, 2, 4, 14, 124, 14992 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS An intersecting set-system is a finite set of finite nonempty sets (edges), any two of which have a nonempty intersection. LINKS Table of n, a(n) for n=0..5. EXAMPLE Non-isomorphic representatives of the a(3) = 14 intersecting set-systems: {} {{1}} {{1,2}} {{1,2,3}} {{2},{1,2}} {{3},{1,2,3}} {{1,3},{2,3}} {{2,3},{1,2,3}} {{3},{1,3},{2,3}} {{3},{2,3},{1,2,3}} {{1,2},{1,3},{2,3}} {{1,3},{2,3},{1,2,3}} {{3},{1,3},{2,3},{1,2,3}} {{1,2},{1,3},{2,3},{1,2,3}} CROSSREFS Cf. A001206, A006126, A051185, A261006, A283877, A304982, A304996, A304998, A305843, A305844, A305854-A305857. Sequence in context: A102449 A193520 A102897 * A001527 A067209 A134040 Adjacent sequences: A305853 A305854 A305855 * A305857 A305858 A305859 KEYWORD nonn,more AUTHOR Gus Wiseman, Jun 11 2018 EXTENSIONS a(5) from Andrew Howroyd, Aug 12 2019 STATUS approved

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Last modified August 15 11:39 EDT 2024. Contains 375173 sequences. (Running on oeis4.)