OFFSET
1,6
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
Alois P. Heinz, Table of n, a(n) for n = 1..65536
EXAMPLE
60060 has 7 prime indices {1,1,2,3,4,5,6}, all of which divide 60060, and 6 of which are distinct, so a(60060) = 6.
MAPLE
a:= n-> add(`if`(irem(n, numtheory[pi](i[1]))=0, 1, 0), i=ifactors(n)[2]):
seq(a(n), n=1..120); # Alois P. Heinz, Mar 19 2019
MATHEMATICA
Table[Count[If[n==1, {}, FactorInteger[n]], {p_, _}/; Divisible[n, PrimePi[p]]], {n, 100}]
PROG
(PARI) a(n) = {my(f = factor(n)[, 1]); sum(k=1, #f, !(n % primepi(f[k]))); } \\ Michel Marcus, Mar 19 2019
CROSSREFS
KEYWORD
nonn
AUTHOR
Gus Wiseman, Mar 18 2019
STATUS
approved