OFFSET
1,3
COMMENTS
A prime index of n is a number m such that prime(m) divides n.
EXAMPLE
The 19th squarefree number is 30 with prime indices (3,2,1), so a(19) = 6.
MATHEMATICA
Table[Total[Cases[FactorInteger[n], {p_, k_}:>k*PrimePi[p]]], {n, Select[Range[100], SquareFreeQ]}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Gus Wiseman, Sep 15 2018
STATUS
approved