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 A156875 Number of safe primes <= n. 8
 0, 0, 0, 0, 1, 1, 2, 2, 2, 2, 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, 4, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,7 COMMENTS a(n) = SUM(A156659(k): 1<=k<=n); a(n) = A156874(floor((n-1)\2)). LINKS R. Zumkeller, Table of n, a(n) for n = 1..10000 Wikipedia, Safe prime EXAMPLE a(120) = #{5, 7, 11, 23, 47, 59, 83, 107} = 8. CROSSREFS A005385, A156874, A156876, A156877, A156878, A000720. Sequence in context: A084558 A320065 A163291 * A066339 A052375 A212625 Adjacent sequences:  A156872 A156873 A156874 * A156876 A156877 A156878 KEYWORD nonn AUTHOR Reinhard Zumkeller, Feb 18 2009 STATUS approved

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Last modified January 18 16:40 EST 2019. Contains 319271 sequences. (Running on oeis4.)