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 A317795 Number of non-isomorphic set-systems spanning n vertices with no singletons. 14
 1, 0, 1, 6, 172, 611852, 200253853704512, 263735716028826427334553305221120, 5609038300883759793482640992086670066496449147691597380832361377955840 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,4 LINKS Table of n, a(n) for n=0..8. EXAMPLE Non-isomorphic representatives of the a(3) = 6 set-systems: {123} {12}{13} {12}{123} {12}{13}{23} {12}{13}{123} {12}{13}{23}{123} MATHEMATICA sysnorm[{}]:={}; sysnorm[m_]:=If[Union@@m!=Range[Max@@Flatten[m]], sysnorm[m/.Rule@@@Table[{(Union@@m)[[i]], i}, {i, Length[Union@@m]}]], First[Sort[sysnorm[m, 1]]]]; sysnorm[m_, aft_]:=If[Length[Union@@m]<=aft, {m}, With[{mx=Table[Count[m, i, {2}], {i, Select[Union@@m, #>=aft&]}]}, Union@@(sysnorm[#, aft+1]&/@Union[Table[Map[Sort, m/.{par+aft-1->aft, aft->par+aft-1}, {0, 1}], {par, First/@Position[mx, Max[mx]]}]])]]; Table[Length[Union[sysnorm/@Select[Subsets[Select[Subsets[Range[n]], Length[#]>1&]], Union@@#==Range[n]&]]], {n, 4}] CROSSREFS First differences of A317794. Cf. A000088, A000612, A003180, A007716, A055621, A283877, A300913, A306005, A317533, A317757, A319876. Sequence in context: A266852 A266311 A323820 * A166762 A323279 A214801 Adjacent sequences: A317792 A317793 A317794 * A317796 A317797 A317798 KEYWORD nonn AUTHOR Gus Wiseman, Aug 07 2018 EXTENSIONS More terms from Gus Wiseman, Dec 13 2018 STATUS approved

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Last modified April 25 09:56 EDT 2024. Contains 371967 sequences. (Running on oeis4.)