OFFSET

1,5

COMMENTS

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

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

KEYWORD

nonn

AUTHOR

Felix FrÃ¶hlich, May 03 2021

STATUS

approved