This site is supported by donations to The OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A326907 Number of non-isomorphic sets of subsets of {1..n} that are closed under union and cover all n vertices. First differences of A193675. 5
 2, 2, 6, 28, 330, 28960, 216562364, 5592326182940100 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 COMMENTS Differs from A108800 in having a(0) = 2 instead of 1. LINKS EXAMPLE Non-isomorphic representatives of the a(0) = 2 through a(3) = 28 sets of sets:   {}    {{1}}    {{12}}          {{123}}   {{}}  {{}{1}}  {{}{12}}        {{}{123}}                  {{2}{12}}       {{3}{123}}                  {{}{2}{12}}     {{23}{123}}                  {{1}{2}{12}}    {{}{3}{123}}                  {{}{1}{2}{12}}  {{}{23}{123}}                                  {{1}{23}{123}}                                  {{3}{23}{123}}                                  {{13}{23}{123}}                                  {{}{1}{23}{123}}                                  {{}{3}{23}{123}}                                  {{}{13}{23}{123}}                                  {{2}{3}{23}{123}}                                  {{2}{13}{23}{123}}                                  {{3}{13}{23}{123}}                                  {{12}{13}{23}{123}}                                  {{}{2}{3}{23}{123}}                                  {{}{2}{13}{23}{123}}                                  {{}{3}{13}{23}{123}}                                  {{}{12}{13}{23}{123}}                                  {{2}{3}{13}{23}{123}}                                  {{3}{12}{13}{23}{123}}                                  {{}{2}{3}{13}{23}{123}}                                  {{}{3}{12}{13}{23}{123}}                                  {{2}{3}{12}{13}{23}{123}}                                  {{}{2}{3}{12}{13}{23}{123}}                                  {{1}{2}{3}{12}{13}{23}{123}}                                  {{}{1}{2}{3}{12}{13}{23}{123}} CROSSREFS The case without empty sets is A108798. The case with a single covering edge is A108800. First differences of A193675. The case also closed under intersection is A326898 for n > 0. The labeled version is A326906. The same for union instead of intersection is (also) A326907. Cf. A001930, A102895, A108798, A193674, A193675, A326880, A326881, A326883, A326898, A326908. Sequence in context: A214446 A179320 A004304 * A270487 A058250 A179929 Adjacent sequences:  A326904 A326905 A326906 * A326908 A326909 A326910 KEYWORD nonn,more AUTHOR Gus Wiseman, Aug 03 2019 EXTENSIONS a(7) added from A108800 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 October 20 02:54 EDT 2019. Contains 328244 sequences. (Running on oeis4.)