A156877 Number of primes <= n that are safe primes and also Sophie Germain primes.

0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4

Offset

1,11

Links

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

Formula

a(n) = A156874(n) + A156875(n) - A156876(n).

a(n) = Sum_{k=1..n} A156659(k)*A156660(k).

Example

a(120) = #{5, 11, 23, 83} = 4.

Crossrefs

Cf. A059455, A005384, A005385, A000720.

Cf. A156874, A156875, A156876, A156659, A156660.

Sequence in context: A074594 A211667 A001069 * A110591 A105209 A179076

Adjacent sequences: A156874 A156875 A156876 * A156878 A156879 A156880

Keyword

nonn

Author

Reinhard Zumkeller, Feb 18 2009

Status

approved