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 A329557 Smallest MM-number of a set of n nonempty sets. 8
 1, 3, 15, 165, 2145, 36465, 1057485 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS A prime index of n is a number m such that prime(m) divides n. The multiset of prime indices of n is row n of A112798. The multiset of multisets with MM-number n is formed by taking the multiset of prime indices of each part of the multiset of prime indices of n. For example, the prime indices of 78 are {1,2,6}, so the multiset of multisets with MM-number 78 is {{},{1},{1,2}}. LINKS FORMULA a(n) = A329558(n + 1)/2. EXAMPLE The sequence of terms together with their corresponding systems begins:         1: {}         3: {{1}}        15: {{1},{2}}       165: {{1},{2},{3}}      2145: {{1},{2},{3},{1,2}}     36465: {{1},{2},{3},{1,2},{4}}   1057485: {{1},{2},{3},{1,2},{4},{1,3}} MATHEMATICA primeMS[n_]:=If[n==1, {}, Flatten[Cases[FactorInteger[n], {p_, k_}:>Table[PrimePi[p], {k}]]]]; dae=Select[Range[10000], SquareFreeQ[#]&&And@@SquareFreeQ/@primeMS[#]&&FreeQ[primeMS[#], 1]&]; Table[dae[[Position[PrimeOmega/@dae, k][[1, 1]]]], {k, First[Split[Union[PrimeOmega/@dae], #2==#1+1&]]}] CROSSREFS MM-numbers of sets of sets are A302494. MM-numbers of sets of nonempty sets are A329629. The version allowing empty sets is A329558. The version without singletons is A329554. Cf. A056239, A072639, A112798, A302242, A326031, A329552, A329555, A329556. Other MM-numbers: A305078 (connected), A316476 (antichains), A318991 (chains), A320456 (covers), A329559 (clutters). Sequence in context: A005016 A304998 A105611 * A108975 A097489 A080696 Adjacent sequences:  A329554 A329555 A329556 * A329558 A329559 A329560 KEYWORD nonn,more AUTHOR Gus Wiseman, Nov 17 2019 STATUS approved

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Last modified May 14 05:29 EDT 2021. Contains 343872 sequences. (Running on oeis4.)