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 A156877 Number of primes <= 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 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

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Last modified October 2 16:46 EDT 2023. Contains 365837 sequences. (Running on oeis4.)