A336388 Number of prime divisors of sigma(n) that divide n; a(1) = 0.
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
Keywords
Links
Programs
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PARI
A336388(n) = if(1==n,0,#select(p -> !(n%p), factor(sigma(n))[, 1]));
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.