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A185192
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Number of primes less than 2^n.
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3
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0, 2, 4, 6, 11, 18, 31, 54, 97, 172, 309, 564, 1028, 1900, 3512, 6542, 12251, 23000, 43390, 82025, 155611, 295947, 564163, 1077871, 2063689, 3957809, 7603553, 14630843, 28192750, 54400028, 105097565, 203280221, 393615806, 762939111, 1480206279, 2874398515
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OFFSET
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1,2
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COMMENTS
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This sequence differs from A007053 in the offset and in that the latter includes 1 (since the prime 2 is equal to 2^1, not less than it).
Number of primes with at most n bits.
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LINKS
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David Baugh, Table of n, a(n) for n = 1..90 (terms n = 1..81 from Charles R Greathouse IV). See A007053 for additional information.
Wikipedia, Prime-counting function
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FORMULA
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a(n) = A000720(2^n - 1).
a(n) = A007053(n) for n > 1.
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EXAMPLE
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a(7) = 31 because prime(31) = 127, prime(32) = 131, and 127 < 2^7 < 131.
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MATHEMATICA
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PrimePi[2^Range[32] - 1] (* Alonso del Arte, May 05 2019 *)
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PROG
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(PARI) a(n)=primepi(2^n-1) \\ Charles R Greathouse IV, Dec 04 2014
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CROSSREFS
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Cf. A000720, A006880, A007053, A014234.
Sequence in context: A131298 A168445 A328669 * A007053 A005684 A260697
Adjacent sequences: A185189 A185190 A185191 * A185193 A185194 A185195
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KEYWORD
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nonn,hard
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AUTHOR
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Washington Bomfim, Jan 23 2012
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STATUS
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approved
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