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A336388
Number of prime divisors of sigma(n) that divide n; a(1) = 0.
2
0, 0, 0, 0, 0, 2, 0, 0, 0, 1, 0, 1, 0, 1, 1, 0, 0, 1, 0, 1, 0, 1, 0, 2, 0, 1, 0, 2, 0, 2, 0, 0, 1, 1, 0, 0, 0, 1, 0, 2, 0, 2, 0, 1, 1, 1, 0, 1, 0, 0, 1, 1, 0, 2, 0, 1, 0, 1, 0, 2, 0, 1, 0, 0, 0, 2, 0, 1, 1, 1, 0, 1, 0, 1, 0, 1, 0, 2, 0, 1, 0, 1, 0, 2, 0, 1, 1, 1, 0, 2, 1, 1, 0, 1, 1, 2, 0, 0, 1, 0, 0, 2, 0, 1, 1
OFFSET
1,6
FORMULA
a(n) = Sum_{p over distinct primes dividing sigma(n)} [p|n], where [ ] is the Iverson bracket, giving in this case 1 only if p divides n, and 0 otherwise.
PROG
(PARI) A336388(n) = if(1==n, 0, #select(p -> !(n%p), factor(sigma(n))[, 1]));
CROSSREFS
Cf. also A173438, A336352, A336387.
Sequence in context: A321013 A284258 A322389 * A277735 A248911 A116681
KEYWORD
nonn
AUTHOR
Antti Karttunen, Jul 25 2020
STATUS
approved