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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
Wikipedia, Safe prime
EXAMPLE
a(120) = #{5, 7, 11, 23, 47, 59, 83, 107} = 8.
CROSSREFS
Sequence in context: A084558 A320065 A163291 * A066339 A345379 A052375
KEYWORD
nonn
AUTHOR
Reinhard Zumkeller, Feb 18 2009
STATUS
approved

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Last modified March 28 18:04 EDT 2024. Contains 371254 sequences. (Running on oeis4.)