OFFSET

1,12

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.

LINKS

EXAMPLE

For example, the prime indices of 22770 are {1,2,2,3,5,9}, with differences (1,0,1,2,4), so a(22770) = 4.

MATHEMATICA

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

Table[Length[Union[Differences[primeMS[n]]]], {n, 1000}]

CROSSREFS

Crossrefs found in the link are not repeated here.

A287352 lists differences between 0-prepended prime indices.

A355534 lists augmented differences between prime indices.

A355536 lists differences between prime indices.

KEYWORD

nonn

AUTHOR

Gus Wiseman, Jul 10 2022

STATUS

approved