

A007053


Number of primes <= 2^n.
(Formerly M1018)


75



0, 1, 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, 5586502348, 10866266172, 21151907950, 41203088796, 80316571436, 156661034233, 305761713237, 597116381732, 1166746786182, 2280998753949, 4461632979717, 8731188863470, 17094432576778, 33483379603407, 65612899915304, 128625503610475
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OFFSET

0,3


COMMENTS

Conjecture: The number 4 is the only perfect power in this sequence. In other words, it is impossible to have a(n) = x^m for some integers n > 3, m > 1 and x > 1.  ZhiWei Sun, Sep 30, 2015


REFERENCES

Jens Franke et al., pi(10^24), Posting to the Number Theory Mailing List, Jul 29 2010
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).


LINKS

Charles R Greathouse IV and Douglas B. Staple, Table of n, a(n) for n = 0..86 [a(0)a(75) from Tomás Oliveira e Silva, a(76)a(77) from Jens Franke et al., Jul 29 2010, a(78)a(80) from Jens Franke et al. on the RH, verified unconditionally by Douglas B. Staple, and a(81)a(86) from Douglas B. Staple]
Andrew R. Booker, The Nth Prime Page
S. W. Golomb, Letter to N. J. A. Sloane, Jul. 1991
Thomas R. Nicely, Some Results of Computational Research in Prime Numbers
Tomás Oliveira e Silva, Tables of values of pi(x) and of pi2(x)
Tomás Oliveira e Silva, Computing pi(x): the combinatorial method, Revista Do Detua, Vol. 4, No 6, March 2006.
Douglas B. Staple, The combinatorial algorithm for computing pi(x), preprint, 2015.
Index entries for sequences related to numbers of primes in various ranges


FORMULA

a(n) = A060967(2n).  R. J. Mathar, Sep 15 2012


EXAMPLE

pi(2^3)=4 since first 4 primes are 2,3,5,7 all <=2^3=8.


MATHEMATICA

Table[PrimePi[2^n], {n, 0, 46}] (* Robert G. Wilson v *)


PROG

(PARI) a(n) = primepi(1<<n); \\ John W. Nicholson, May 16 2011


CROSSREFS

Cf. A006880, A036378.
Sequence in context: A131298 A168445 A185192 * A005684 A260697 A018167
Adjacent sequences: A007050 A007051 A007052 * A007054 A007055 A007056


KEYWORD

nonn,nice


AUTHOR

N. J. A. Sloane, Mira Bernstein, Robert G. Wilson v, S. W. Golomb


EXTENSIONS

More terms from Jud McCranie
Extended to n = 52 by Warren D. Smith, Dec 11 2000, computed with MeisselLehmerLegendre inclusion exclusion formula code he wrote back in 1985, recently rerun.
Extended to n = 86 by Douglas B. Staple, Dec 18 2014


STATUS

approved



