A140888 Number of nonprimes in [210n - 210, 210n] coprime to 210.

6, 13, 15, 16, 18, 19, 21, 17, 21, 21, 22, 23, 18, 22, 26, 21, 22, 21, 24, 24, 22, 25, 22, 22, 26, 24, 22, 21, 28, 23, 25, 23, 25, 24, 26, 25, 22, 27, 27, 24, 27, 22, 24, 25, 23, 26, 23, 28, 23, 26, 27, 26, 27, 26, 27, 30, 22, 26, 27, 22, 25, 24, 26, 29, 27, 24, 27, 31, 25, 26

Offset: 1

Author

Juri-Stepan Gerasimov, Jul 06 2008

Keywords

• nonn
• easy
• less

Comments

For almost all n, a(n) = phi(210) = 48. It first attains this value at a(1751794).

Examples

			{1,11,13,...,209,} are coprime to 210 in [0, 210]; the nonprimes are {1,121,143,169,187,209} so a(1) = 1.
		

Crossrefs

Cf. A008364, A140887.

Programs

PARI

a(n)=sum(k=210*n-210,210*n,gcd(k,210)==1&!isprime(k))

Extensions

Corrected and rewritten by Charles R Greathouse IV, Mar 26 2010