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

1,7

Comments

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

Links

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

Example

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.

Crossrefs

Cf. A048597.

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

Sequence in context: A354666 A110298 A362379 * A283272 A292166 A282192

Adjacent sequences: A144737 A144738 A144739 * A144741 A144742 A144743

Keyword

easy,nonn

Author

Reikku Kulon, Sep 20 2008

Status

approved