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A156877 Number of primes <= n that are safe primes and also Sophie Germain primes. 5

%I #9 Nov 06 2022 07:48:17

%S 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,

%T 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,

%U 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

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

%H Reinhard Zumkeller, <a href="/A156877/b156877.txt">Table of n, a(n) for n = 1..10000</a>

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

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

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

%Y Cf. A059455, A005384, A005385, A000720.

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

%K nonn

%O 1,11

%A _Reinhard Zumkeller_, Feb 18 2009

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Last modified March 29 06:15 EDT 2024. Contains 371265 sequences. (Running on oeis4.)