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 A305854 Number of unlabeled spanning intersecting set-systems on n vertices. 41
 1, 1, 2, 10, 110, 14868 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS An intersecting set-system S is a finite set of finite nonempty sets (edges), any two of which have a nonempty intersection. S is spanning if every vertex is contained in some edge. LINKS Table of n, a(n) for n=0..5. FORMULA a(n) = A305856(n) - A305856(n-1) for n > 0. - Andrew Howroyd, Aug 12 2019 EXAMPLE Non-isomorphic representatives of the a(3) = 10 spanning intersecting set-systems: {{1,2,3}} {{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, A304998, A305843, A305844, A305855-A305857. Sequence in context: A181445 A231969 A062499 * A234296 A049505 A136518 Adjacent sequences: A305851 A305852 A305853 * A305855 A305856 A305857 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 June 8 11:34 EDT 2023. Contains 363164 sequences. (Running on oeis4.)