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A356939
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MM-numbers of multisets of intervals. Products of primes indexed by members of A073485.
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9
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1, 2, 3, 4, 5, 6, 8, 9, 10, 11, 12, 13, 15, 16, 17, 18, 20, 22, 24, 25, 26, 27, 30, 31, 32, 33, 34, 36, 39, 40, 41, 44, 45, 47, 48, 50, 51, 52, 54, 55, 59, 60, 62, 64, 65, 66, 67, 68, 72, 75, 78, 80, 81, 82, 83, 85, 88, 90, 93, 94, 96, 99, 100, 102, 104, 108
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OFFSET
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1,2
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COMMENTS
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An interval such as {3,4,5} is a set of positive integers with all differences of adjacent elements equal to 1.
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.
We define the multiset of multisets with MM-number n to be formed by taking the multiset of prime indices of each part of the multiset of prime indices of n. The size of this multiset of multisets is A302242(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}}.
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LINKS
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EXAMPLE
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The initial terms and corresponding multisets of multisets:
1: {}
2: {{}}
3: {{1}}
4: {{},{}}
5: {{2}}
6: {{},{1}}
8: {{},{},{}}
9: {{1},{1}}
10: {{},{2}}
11: {{3}}
12: {{},{},{1}}
13: {{1,2}}
15: {{1},{2}}
16: {{},{},{},{}}
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MATHEMATICA
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primeMS[n_]:=If[n==1, {}, Flatten[Cases[FactorInteger[n], {p_, k_}:>Table[PrimePi[p], {k}]]]];
chQ[y_]:=Or[Length[y]<=1, Union[Differences[y]]=={1}];
Select[Range[100], And@@chQ/@primeMS/@primeMS[#]&]
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CROSSREFS
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A000688 counts factorizations into prime powers.
A001222 counts prime factors with multiplicity.
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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