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 A108800 Number of nonisomorphic systems enumerated by A102895. 15
 1, 2, 6, 28, 330, 28960, 216562364, 5592326182940100 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS Also the number of non-isomorphic sets of sets with {} that are closed under intersection. Also the number of non-isomorphic set-systems (without {}) covering n + 1 vertices and closed under intersection. - Gus Wiseman, Aug 05 2019 LINKS M. Habib and L. Nourine, The number of Moore families on n = 6, Discrete Math., 294 (2005), 291-296. FORMULA a(n > 0) = 2 * A108798(n). EXAMPLE From Gus Wiseman, Aug 02 2019: (Start) Non-isomorphic representatives of the a(0) = 1 through a(3) = 28 sets of sets with {} that are closed under intersection:   {}  {}     {}            {}       {}{1}  {}{1}         {}{1}              {}{12}        {}{12}              {}{1}{2}      {}{123}              {}{2}{12}     {}{1}{2}              {}{1}{2}{12}  {}{1}{23}                            {}{2}{12}                            {}{3}{123}                            {}{1}{2}{3}                            {}{23}{123}                            {}{1}{2}{12}                            {}{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} (End) CROSSREFS Except a(0) = 1, first differences of A193675. The connected case (i.e., with maximum) is A108798. The same for union instead of intersection is (also) A108798. The labeled version is A102895. The case also closed under union is A326898. The covering case is A326883. Cf. A001930, A102894, A102896, A102897, A193674, A326880, A326881. Sequence in context: A002047 A126340 A277480 * A325507 A306793 A326359 Adjacent sequences:  A108797 A108798 A108799 * A108801 A108802 A108803 KEYWORD nonn,more AUTHOR Don Knuth, Jul 01 2005 EXTENSIONS a(6) added (using A193675) by N. J. A. Sloane, Aug 02 2011 Changed a(0) from 2 to 1 by Gus Wiseman, Aug 02 2019 a(7) added (using A108798) by Andrew Howroyd, Aug 10 2019 STATUS approved

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Last modified June 23 09:00 EDT 2021. Contains 345395 sequences. (Running on oeis4.)