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

1,17

Links

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

Formula

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

Example

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

Crossrefs

Cf. A059500, A005384, A005385.

Cf. A000720, A156876.

Sequence in context: A010096 A230864 A063510 * A214454 A140474 A091195

Adjacent sequences: A156875 A156876 A156877 * A156879 A156880 A156881

Keyword

nonn

Author

Reinhard Zumkeller, Feb 18 2009

Status

approved