This site is supported by donations to The OEIS Foundation.

 Please make a donation to keep the OEIS running. We are now in our 55th year. In the past year we added 12000 new sequences and reached 8000 citations (which often say "discovered thanks to the OEIS"). We need to raise money to hire someone to manage submissions, which would reduce the load on our editors and speed up editing. Other ways to donate

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified December 9 09:21 EST 2019. Contains 329877 sequences. (Running on oeis4.)