A368094 Number of non-isomorphic set-systems of weight n contradicting a strict version of the axiom of choice.
0, 0, 0, 0, 1, 1, 5, 12, 36, 97, 291
Offset: 0
Examples
Non-isomorphic representatives of the a(5) = 1 through a(7) = 12 set-systems: {{1},{2},{3},{2,3}} {{1},{2},{1,3},{2,3}} {{1},{2},{1,2},{3,4,5}} {{1},{2},{3},{1,2,3}} {{1},{3},{2,3},{1,2,3}} {{2},{3},{1,3},{2,3}} {{1},{4},{1,4},{2,3,4}} {{3},{4},{1,2},{3,4}} {{2},{3},{2,3},{1,2,3}} {{1},{2},{3},{4},{3,4}} {{3},{1,2},{1,3},{2,3}} {{1},{2},{3},{1,3},{2,3}} {{1},{2},{3},{2,4},{3,4}} {{1},{2},{3},{4},{2,3,4}} {{1},{3},{4},{2,4},{3,4}} {{1},{4},{5},{2,3},{4,5}} {{2},{3},{4},{1,2},{3,4}} {{1},{2},{3},{4},{5},{4,5}}
Links
- Wikipedia, Axiom of choice.
Crossrefs
Programs
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Mathematica
sps[{}]:={{}};sps[set:{i_,_}]:=Join@@Function[s,Prepend[#,s]& /@ sps[Complement[set,s]]] /@ Cases[Subsets[set],{i,_}]; mpm[n_]:=Join@@Table[Union[Sort[Sort/@(#/.x_Integer:>s[[x]])]& /@ sps[Range[n]]], {s,Flatten[MapIndexed[Table[#2,{#1}]&,#]]& /@ IntegerPartitions[n]}]; brute[m_]:=First[Sort[Table[Sort[Sort /@ (m/.Rule@@@Table[{i,p[[i]]},{i,Length[p]}])], {p,Permutations[Union@@m]}]]]; Table[Length[Union[brute/@Select[mpm[n], UnsameQ@@#&&And@@UnsameQ@@@# && Select[Tuples[#], UnsameQ@@#&]=={}&]]],{n,0,8}]
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