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A144740 Partial totient function phi(c, n) for c = 2: number of semiprimes less than and coprime to n. 4
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 (list; graph; refs; listen; history; text; internal format)
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: A124220 A221755 A110298 * A283272 A292166 A282192

Adjacent sequences:  A144737 A144738 A144739 * A144741 A144742 A144743

KEYWORD

easy,nonn

AUTHOR

Reikku Kulon, Sep 20 2008

STATUS

approved

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Last modified February 23 02:43 EST 2018. Contains 299473 sequences. (Running on oeis4.)