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A156877 Number of numbers <= n that are safe primes and also Sophie Germain primes. 5
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,11

COMMENTS

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

a(n) = SUM(A156659(k)*A156660(k): 1<=k<=n).

LINKS

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

EXAMPLE

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

CROSSREFS

A059455, A005384, A005385, A000720.

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

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Last modified January 25 03:49 EST 2020. Contains 331241 sequences. (Running on oeis4.)