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a(n) = gcd(n, A064988(n)).
3

%I #8 Sep 12 2018 10:48:42

%S 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,

%T 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,

%U 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

%N a(n) = gcd(n, A064988(n)).

%C 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).

%H Antti Karttunen, <a href="/A318668/b318668.txt">Table of n, a(n) for n = 1..65537</a>

%H <a href="/index/Pri#prime_indices">Index entries for sequences computed from indices in prime factorization</a>

%F a(n) = gcd(n, A064988(n)).

%o (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.

%Y Cf. A064988, A318660.

%K nonn

%O 1,6

%A _Antti Karttunen_, Sep 11 2018