A156878 Number of primes <= n that are neither safe primes and nor Sophie Germain primes.

0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 2, 2, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 5, 5, 5, 5, 5, 5, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 7, 7, 7, 7, 7, 7, 8, 8, 8, 8, 9, 9, 10, 10, 10, 10, 10, 10, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11

Offset: 1

Author

Reinhard Zumkeller, Feb 18 2009

Keywords

• nonn

Examples

			a(120) = #{13,17,19,31,37,43,61,67,71,73,79,97,10,103,109} = 15.
		

Links

• Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A059500, A005384, A005385.

Cf. A000720, A156876.

Formula

a(n) = A000720(n) - A156876(n).