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.
EXAMPLE
The a(n) gapless divisors of n = 1..24:
1 2 1 4 1 6 1 8 1 2 1 12 1 2 1 16 1 18 1 4 1 2 1 24
1 2 2 4 1 6 1 8 6 2 1 12
1 1 2 4 4 2 1 8
1 2 2 1 6
1 1 4
2
1
For example, the divisors of 12 are {1,2,3,4,6,12}, of which {1,2,4,6,12} belong to A055932, so a(12) = 5.
MATHEMATICA
primeMS[n_]:=If[n==1, {}, Flatten[Cases[FactorInteger[n], {p_, k_}:>Table[PrimePi[p], {k}]]]];
normQ[m_]:=m=={}||Union[m]==Range[Max[m]];
Table[Length[Select[Divisors[n], normQ[primeMS[#]]&]], {n, 100}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Gus Wiseman, Aug 04 2022
STATUS
approved