OFFSET
1,2
LINKS
FORMULA
Multiplicative with a(p^e) = p^e if (p^(1+e) - 1)/(p-1) = 1 + p + p^2 + ... + p^e is prime, and 1 otherwise.
a(n) = n / A324894(n).
EXAMPLE
For n = 150 = 2 * 3 * 5^2, sigma(2) = 3 is a prime, sigma(3) = 4 is not prime, and sigma(25) = 31 is a prime, thus a(150) = 2 * 25 = 50.
PROG
CROSSREFS
KEYWORD
nonn,mult
AUTHOR
Antti Karttunen, Mar 29 2019
STATUS
approved