login
A318668
a(n) = gcd(n, A064988(n)).
3
1, 1, 1, 1, 1, 3, 1, 1, 1, 1, 1, 3, 1, 1, 5, 1, 1, 3, 1, 1, 1, 1, 1, 3, 1, 1, 1, 1, 1, 15, 1, 1, 1, 1, 1, 9, 1, 1, 1, 1, 1, 3, 1, 1, 5, 1, 1, 3, 1, 1, 1, 1, 1, 3, 11, 1, 1, 1, 1, 15, 1, 1, 1, 1, 1, 3, 1, 1, 1, 1, 1, 9, 1, 1, 5, 1, 1, 3, 1, 1, 1, 1, 1, 3, 1, 1, 1, 1, 1, 15, 1, 1, 1, 1, 1, 3, 1, 1, 1, 1, 1, 3, 1, 1, 5
OFFSET
1,6
COMMENTS
a(n) > 1 if and only if the prime factorization of n contains at least two distinct primes, p and q, such that q = prime(p).
FORMULA
a(n) = gcd(n, A064988(n)).
PROG
(PARI) A318668(n) = { my(f = factor(n)); for (k=1, #f~, f[k, 1] = prime(f[k, 1]); ); gcd(n, factorback(f)); }; \\ After code in A064988.
CROSSREFS
Sequence in context: A214071 A226915 A180173 * A322361 A219208 A336850
KEYWORD
nonn
AUTHOR
Antti Karttunen, Sep 11 2018
STATUS
approved