A144765 Number of triprimes less than or equal to and not coprime to n.

0, 0, 0, 0, 0, 0, 0, 1, 0, 1, 0, 2, 0, 2, 1, 2, 0, 3, 0, 4, 2, 4, 0, 4, 1, 4, 3, 5, 0, 7, 0, 6, 4, 6, 3, 7, 0, 6, 4, 6, 0, 8, 0, 8, 7, 8, 0, 10, 2, 10, 6, 10, 0, 12, 5, 10, 6, 10, 0, 12, 0, 10, 8, 10, 5, 14, 0, 12, 8, 15, 0, 16, 0, 13, 12, 14, 6, 19, 0, 17, 10, 15, 0, 19, 7, 15, 10, 15, 0, 19, 6, 16

Offset: 1

Author

Reikku Kulon, Sep 20 2008

Keywords

• easy
• nonn

Crossrefs

Cf. A000010, A014612, A144741.

Programs

PARI

a(n) = sum(k=1, n, if (bigomega(k) == 3, gcd(k,n) != 1)); \\ Michel Marcus, Apr 15 2023