A319899 Numbers whose number of prime factors with multiplicity (A001222) is the number of distinct prime factors (A001221) in the product of the prime indices (A003963).

1, 3, 5, 7, 11, 15, 17, 19, 23, 26, 31, 33, 35, 39, 41, 51, 53, 55, 58, 59, 65, 67, 69, 74, 77, 83, 85, 86, 87, 91, 93, 94, 95, 97, 103, 109, 111, 119, 122, 123, 127, 129, 131, 142, 146, 155, 157, 158, 161, 165, 169, 177, 178, 179, 183, 185, 187, 191, 201, 202

Offset

1,2

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 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}}. This sequence lists all MM-numbers of square multiset multisystems, meaning the number of edges is equal to the number of distinct vertices.

Links

Table of n, a(n) for n=1..60.

Example

The sequence of multiset multisystems whose MM-numbers belong to the sequence begins:
   1: {}
   3: {{1}}
   5: {{2}}
   7: {{1,1}}
  11: {{3}}
  15: {{1},{2}}
  17: {{4}}
  19: {{1,1,1}}
  23: {{2,2}}
  26: {{},{1,2}}
  31: {{5}}
  33: {{1},{3}}
  35: {{2},{1,1}}
  39: {{1},{1,2}}
  41: {{6}}
  51: {{1},{4}}
  53: {{1,1,1,1}}
  55: {{2},{3}}
  58: {{},{1,3}}
  59: {{7}}
  65: {{2},{1,2}}
  67: {{8}}
  69: {{1},{2,2}}
  74: {{},{1,1,2}}

Mathematica

primeMS[n_]:=If[n==1, {}, Flatten[Cases[FactorInteger[n], {p_, k_}:>Table[PrimePi[p], {k}]]]];
Select[Range[100], PrimeOmega[#]==PrimeNu[Times@@primeMS[#]]&]

Crossrefs

Cf. A003963, A057151, A064573, A120732, A319616, A319877, A320325, A322527, A322530.

Sequence in context: A111622 A356065 A082418 * A085493 A343621 A139252

Adjacent sequences: A319896 A319897 A319898 * A319900 A319901 A319902

Keyword

nonn

Author

Gus Wiseman, Dec 17 2018

Status

approved