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Number of non-isomorphic set multipartitions of weight n satisfying a strict version of the axiom of choice.
10

%I #6 Dec 27 2023 09:41:11

%S 1,1,2,4,9,18,43,95,233,569

%N Number of non-isomorphic set multipartitions of weight n satisfying a strict version of the axiom of choice.

%C A set multipartition is a finite multiset of finite nonempty sets. The weight of a set multipartition is the sum of cardinalities of its elements. Weight is generally not the same as number of vertices.

%C The axiom of choice says that, given any sequence of nonempty sets, it is possible to choose a sequence containing an element from each. In the strict version, the elements of this sequence must be distinct, meaning none is chosen more than once.

%H Wikipedia, <a href="https://en.wikipedia.org/wiki/Axiom_of_choice">Axiom of choice</a>.

%e Non-isomorphic representatives of the a(1) = 1 through a(5) = 18 set multipartitions:

%e {{1}} {{1,2}} {{1,2,3}} {{1,2,3,4}} {{1,2,3,4,5}}

%e {{1},{2}} {{1},{2,3}} {{1,2},{1,2}} {{1},{2,3,4,5}}

%e {{2},{1,2}} {{1},{2,3,4}} {{1,2},{3,4,5}}

%e {{1},{2},{3}} {{1,2},{3,4}} {{1,4},{2,3,4}}

%e {{1,3},{2,3}} {{2,3},{1,2,3}}

%e {{3},{1,2,3}} {{4},{1,2,3,4}}

%e {{1},{2},{3,4}} {{1},{2,3},{2,3}}

%e {{1},{3},{2,3}} {{1},{2},{3,4,5}}

%e {{1},{2},{3},{4}} {{1},{2,3},{4,5}}

%e {{1},{2,4},{3,4}}

%e {{1},{4},{2,3,4}}

%e {{2},{1,3},{2,3}}

%e {{2},{3},{1,2,3}}

%e {{3},{1,3},{2,3}}

%e {{4},{1,2},{3,4}}

%e {{1},{2},{3},{4,5}}

%e {{1},{2},{4},{3,4}}

%e {{1},{2},{3},{4},{5}}

%t sps[{}]:={{}};sps[set:{i_,___}]:=Join@@Function[s,Prepend[#,s]& /@ sps[Complement[set,s]]]/@Cases[Subsets[set],{i,___}];

%t mpm[n_]:=Join@@Table[Union[Sort[Sort /@ (#/.x_Integer:>s[[x]])]&/@sps[Range[n]]],{s,Flatten[MapIndexed[Table[#2,{#1}]&,#]]& /@ IntegerPartitions[n]}];

%t brute[m_]:=First[Sort[Table[Sort[Sort /@ (m/.Rule@@@Table[{i,p[[i]]},{i,Length[p]}])], {p,Permutations[Union@@m]}]]];

%t Table[Length[Union[brute /@ Select[mpm[n],And@@UnsameQ@@@#&&Select[Tuples[#], UnsameQ@@#&]!={}&]]],{n,0,6}]

%Y The case of unlabeled graphs is A134964, complement A140637.

%Y Set multipartitions have ranks A302478, cf. A073576.

%Y The case of labeled graphs is A133686, complement A367867.

%Y The complement without repeats is A368094 connected A368409.

%Y Without repeats we have A368095, connected A368410.

%Y The complement allowing repeats is A368097, ranks A355529.

%Y Allowing repeated elements gives A368098, ranks A368100.

%Y Factorizations of this type are counted by A368414, complement A368413.

%Y The complement is counted by A368421.

%Y A000110 counts set partitions, non-isomorphic A000041.

%Y A003465 counts covering set-systems, unlabeled A055621.

%Y A007716 counts non-isomorphic multiset partitions, connected A007718.

%Y A058891 counts set-systems, unlabeled A000612, connected A323818.

%Y A283877 counts non-isomorphic set-systems, connected A300913.

%Y Cf. A302545, A306005, A317533, A318360, A367903.

%K nonn,more

%O 0,3

%A _Gus Wiseman_, Dec 26 2023