A144741 Number of semiprimes less than or equal to and not coprime to n.

0, 0, 0, 1, 0, 2, 0, 2, 2, 3, 0, 4, 0, 4, 4, 4, 0, 6, 0, 5, 5, 5, 0, 8, 3, 6, 4, 7, 0, 10, 0, 6, 6, 7, 6, 11, 0, 8, 7, 11, 0, 14, 0, 9, 9, 9, 0, 14, 4, 12, 8, 10, 0, 15, 7, 12, 9, 10, 0, 20, 0, 11, 11, 11, 8, 19, 0, 12, 10, 18, 0, 19, 0, 12, 14, 13, 8, 21, 0, 17, 9, 13, 0, 24, 9, 14, 11, 17, 0, 28, 9

Offset

1,6

Links

Table of n, a(n) for n=1..91.

Example

a(10) = 3: four, six and ten are semiprimes; nine is a semiprime relatively prime to ten.

Prog

(PARI) a(n) = sum(k=1, n, if (bigomega(k) == 2, gcd(k, n) != 1)); \\ Michel Marcus, Apr 15 2023

Crossrefs

Cf. A000010, A001358, A144740.

Sequence in context: A309107 A366353 A366354 * A352965 A103615 A308167

Adjacent sequences: A144738 A144739 A144740 * A144742 A144743 A144744

Keyword

easy,nonn

Author

Reikku Kulon, Sep 20 2008

Status

approved