login
This site is supported by donations to The OEIS Foundation.

 

Logo


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

Table of n, a(n) for n=0..7.

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.

License Agreements, Terms of Use, Privacy Policy. .

Last modified October 15 22:25 EDT 2019. Contains 328038 sequences. (Running on oeis4.)