A144740 Partial totient function phi(c, n) for c = 2: number of semiprimes less than and coprime to n.

0, 0, 0, 0, 1, 0, 2, 0, 1, 1, 4, 0, 4, 1, 2, 2, 6, 0, 6, 1, 2, 3, 8, 0, 6, 4, 6, 3, 10, 0, 10, 4, 5, 5, 7, 2, 13, 6, 8, 4, 15, 1, 15, 6, 6, 7, 16, 2, 13, 5, 10, 8, 18, 3, 12, 7, 11, 11, 21, 1, 21, 11, 11, 11, 15, 4, 23, 11, 14, 6, 24, 5, 24, 13, 11, 12, 18, 5, 26, 9, 17, 14, 27, 3, 19, 15, 19

Offset: 1

Author

Reikku Kulon, Sep 20 2008

Keywords

• easy
• nonn

Comments

phi(c, n) = 0 iff n is in A048597.

Examples

			phi(2, 7) = 2: the two semiprimes less than 7 are 4 and 6.
phi(2, 15) = 2: there are five semiprimes less than 15 (4, 6, 9, 10, 14), but only 4 and 14 are relatively prime to 15.
		

Links

• Reikku Kulon, Table of n, phi(2, n) for n = 1..10000

Crossrefs

Cf. A048597.

Cf. A036997 (phi(n) - max(phi(c, n)) over all nonnegative integers c).