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A322703 Squarefree MM-numbers of strict uniform regular multiset systems spanning an initial interval of positive integers. 3
1, 2, 3, 7, 13, 15, 19, 53, 113, 131, 151, 161, 165, 311, 719, 1291, 1321, 1619, 1937, 1957, 2021, 2093, 2117, 2257, 2805, 3671, 6997, 8161, 10627, 13969, 13987, 14023, 15617, 17719, 17863, 20443, 22207, 22339, 38873, 79349, 84017, 86955, 180503, 202133 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

A multiset multisystem is a finite multiset of finite multisets. 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 multisystem 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 multisystem with MM-number 78 is {{},{1},{1,2}}.

A multiset multisystem is uniform if all parts have the same size, regular if all vertices appear the same number of times, and strict if there are no repeated parts. For example, {{1,1},{2,3},{2,3}} is uniform and regular but not strict, so its MM-number 15463 does not belong to the sequence. Note that the parts of parts such as {1,1} do not have to be distinct, only the multiset of parts.

LINKS

Table of n, a(n) for n=1..44.

EXAMPLE

The sequence of all strict uniform regular multiset multisystems spanning an initial interval of positive integers, together with their MM-numbers, begins:

      1: {}

      2: {{}}

      3: {{1}}

      7: {{1,1}}

     13: {{1,2}}

     15: {{1},{2}}

     19: {{1,1,1}}

     53: {{1,1,1,1}}

    113: {{1,2,3}}

    131: {{1,1,1,1,1}}

    151: {{1,1,2,2}}

    161: {{1,1},{2,2}}

    165: {{1},{2},{3}}

    311: {{1,1,1,1,1,1}}

    719: {{1,1,1,1,1,1,1}}

   1291: {{1,2,3,4}}

   1321: {{1,1,1,2,2,2}}

   1619: {{1,1,1,1,1,1,1,1}}

   1937: {{1,2},{3,4}}

   1957: {{1,1,1},{2,2,2}}

   2021: {{1,4},{2,3}}

   2093: {{1,1},{1,2},{2,2}}

   2117: {{1,3},{2,4}}

   2257: {{1,1,2},{1,2,2}}

   2805: {{1},{2},{3},{4}}

   3671: {{1,1,1,1,1,1,1,1,1}}

   6997: {{1,1,2,2,3,3}}

   8161: {{1,1,1,1,1,1,1,1,1,1}}

  10627: {{1,1,1,1,2,2,2,2}}

  13969: {{1,2,2},{1,3,3}}

  13987: {{1,1,3},{2,2,3}}

  14023: {{1,1,2},{2,3,3}}

  15617: {{1,1},{2,2},{3,3}}

  17719: {{1,2},{1,3},{2,3}}

  17863: {{1,1,1,1,1,1,1,1,1,1,1}}

MATHEMATICA

primeMS[n_]:=If[n==1, {}, Flatten[Cases[FactorInteger[n], {p_, k_}:>Table[PrimePi[p], {k}]]]];

normQ[sys_]:=Or[Length[sys]==0, Union@@sys==Range[Max@@Max@@sys]];

Select[Range[1000], And[SquareFreeQ[#], normQ[primeMS/@primeMS[#]], SameQ@@PrimeOmega/@primeMS[#], SameQ@@Last/@FactorInteger[Times@@primeMS[#]]]&]

CROSSREFS

Cf. A005117, A007016, A112798, A302242, A306017, A306021, A319056, A319189, A319190, A320324, A321698, A321699, A322554, A322833.

Sequence in context: A026472 A286176 A318401 * A225098 A101739 A141633

Adjacent sequences:  A322700 A322701 A322702 * A322704 A322705 A322706

KEYWORD

nonn

AUTHOR

Gus Wiseman, Dec 27 2018

STATUS

approved

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Last modified February 22 12:42 EST 2020. Contains 332136 sequences. (Running on oeis4.)