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 A326883 Number of unlabeled set-systems with {} that are closed under intersection and cover n vertices. 9
 1, 1, 4, 22, 302, 28630, 216533404, 5592325966377736 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 LINKS Table of n, a(n) for n=0..7. FORMULA a(n) = A108800(n) - A108800(n-1) for n > 0. - Andrew Howroyd, Aug 10 2019 EXAMPLE Non-isomorphic representatives of the a(0) = 1 through a(3) = 22 set-systems: {{}} {{}{1}} {{}{12}} {{}{123}} {{}{1}{2}} {{}{1}{23}} {{}{2}{12}} {{}{3}{123}} {{}{1}{2}{12}} {{}{1}{2}{3}} {{}{23}{123}} {{}{1}{3}{23}} {{}{2}{3}{123}} {{}{3}{13}{23}} {{}{1}{23}{123}} {{}{3}{23}{123}} {{}{1}{2}{3}{23}} {{}{1}{2}{3}{123}} {{}{2}{3}{13}{23}} {{}{1}{3}{23}{123}} {{}{2}{3}{23}{123}} {{}{3}{13}{23}{123}} {{}{1}{2}{3}{13}{23}} {{}{1}{2}{3}{23}{123}} {{}{2}{3}{13}{23}{123}} {{}{1}{2}{3}{12}{13}{23}} {{}{1}{2}{3}{13}{23}{123}} {{}{1}{2}{3}{12}{13}{23}{123}} CROSSREFS The case also closed under union is A001930. The connected case (i.e., with maximum) is A108798. The same for union instead of intersection is (also) A108798. The non-covering case is A108800. The labeled case is A326881. Cf. A000798, A102894, A102895, A102897, A193674, A193675, A306445, A326875, A326878, A326880. Sequence in context: A265908 A359111 A119009 * A317803 A053722 A336212 Adjacent sequences: A326880 A326881 A326882 * A326884 A326885 A326886 KEYWORD nonn,more AUTHOR Gus Wiseman, Jul 30 2019 EXTENSIONS a(5)-a(7) from Andrew Howroyd, Aug 10 2019 STATUS approved

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Last modified February 29 16:27 EST 2024. Contains 370425 sequences. (Running on oeis4.)