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 A326908 Number of non-isomorphic sets of subsets of {1..n} that are closed under union and intersection. 4
 2, 4, 9, 23, 70, 256, 1160, 6599, 48017, 452518, 5574706, 90198548, 1919074899, 53620291147, 1962114118390, 93718030190126, 5822768063787557 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 LINKS EXAMPLE Non-isomorphic representatives of the a(0) = 2 through a(3) = 23 sets of subsets:   {}    {}       {}              {}   {{}}  {{}}     {{}}            {{}}         {{1}}    {{1}}           {{1}}         {{}{1}}  {{12}}          {{12}}                  {{}{1}}         {{}{1}}                  {{}{12}}        {{123}}                  {{2}{12}}       {{}{12}}                  {{}{2}{12}}     {{}{123}}                  {{}{1}{2}{12}}  {{2}{12}}                                  {{3}{123}}                                  {{}{2}{12}}                                  {{23}{123}}                                  {{}{3}{123}}                                  {{}{23}{123}}                                  {{}{1}{2}{12}}                                  {{3}{23}{123}}                                  {{}{1}{23}{123}}                                  {{}{3}{23}{123}}                                  {{3}{13}{23}{123}}                                  {{}{2}{3}{23}{123}}                                  {{}{3}{13}{23}{123}}                                  {{}{2}{3}{13}{23}{123}}                                  {{}{1}{2}{3}{12}{13}{23}{123}} MATHEMATICA Table[Length[Select[Subsets[Subsets[Range[n]]], SubsetQ[#, Union@@@Tuples[#, 2]]&&SubsetQ[#, Intersection@@@Tuples[#, 2]]&]], {n, 0, 3}] CROSSREFS The labeled version is A306445. Taking first differences and prepending 1 gives A326898. Taking second differences and prepending two 1's gives A001930. Cf. A000612, A000798, A003180, A108798, A108800, A193675, A326867, A326876, A326878, A326882, A326883. Sequence in context: A125789 A058731 A291981 * A229048 A144309 A080376 Adjacent sequences:  A326905 A326906 A326907 * A326909 A326910 A326911 KEYWORD nonn,more AUTHOR Gus Wiseman, Aug 03 2019 STATUS approved

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Last modified January 19 09:28 EST 2020. Contains 331048 sequences. (Running on oeis4.)