A343901 - OEIS

A343901

a(n) is the number of primes p such that (p-1)|A000010(n).

0, 0, 1, 1, 2, 1, 2, 2, 2, 2, 2, 2, 4, 2, 3, 3, 3, 2, 3, 3, 4, 2, 2, 3, 4, 4, 3, 4, 3, 3, 4, 3, 4, 3, 5, 4, 6, 3, 5, 3, 4, 4, 3, 4, 5, 2, 2, 3, 3, 4, 4, 5, 3, 3, 4, 5, 6, 3, 2, 3, 7, 4, 6, 4, 6, 4, 4, 4, 4, 5, 3, 5, 7, 6, 4, 6, 7, 5, 3, 4, 4, 4, 2, 5, 4, 3, 4

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,5

COMMENTS

Conjecture: a(n) > 0 for n > 2.

LINKS

Table of n, a(n) for n=1..87.

EXAMPLE

For n = 13: A000010(13) = 12 and for p = 2, 3, 5, 7 we have p-1 = 1, 2, 4, 6 and 12 is divisible by each value of p-1, so a(13) = 4.

PROG

(PARI) a(n) = my(e=eulerphi(n), i=0); forprime(p=2, e, if(e%(p-1)==0, i++)); i

CROSSREFS