%I A007053 M1018
%S A007053 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,
%T A007053 762939111,1480206279,2874398515,5586502348,10866266172,21151907950,41203088796,
               80316571436,156661034233,
%U A007053 305761713237,597116381732,1166746786182,2280998753949,4461632979717,8731188863470,
               17094432576778,33483379603407,65612899915304,128625503610475
%N A007053 Number of primes <= 2^n.
%D A007053 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, 
               Academic Press, 1995 (includes this sequence).
%H A007053 N. J. A. Sloane, <a href="b007053.txt">Table of n, a(n) for n=0..75</
               a> (from the web page of Tomas Oliveira e Silva)
%H A007053 Andrew R. Booker, <a href="http://primes.utm.edu/nthprime/">The Nth Prime 
               Page</a>
%H A007053 Thomas R. Nicely, <a href="http://www.trnicely.net/index.html">Some Results 
               of Computational Research in Prime Numbers</a>
%H A007053 Tomas Oliveira e Silva, <a href="http://www.ieeta.pt/~tos/primes.html">
               Tables of values of pi(x) and of pi2(x)</a>
%H A007053 Tomas Oliveira e Silva, <a href="http://www.ieeta.pt/~tos/bib/5.4.pdf">
               Computing (x): the combinatorial method</a>, REVISTA DO DETUA, VOL. 
               4, N 6, MARCH 2006.
%H A007053 <a href="Sindx_Pri.html#primepop">Index entries for sequences related 
               to numbers of primes in various ranges</a>
%e A007053 pi(2^3)=4 since first 4 primes are 2,3,5,7 all <=2^3=8.
%t A007053 Table[PrimePi[2^n], {n, 0, 46}] (* Robert G. Wilson v *)
%Y A007053 Cf. A006880.
%Y A007053 Sequence in context: A026658 A138688 A131298 this_sequence A005684 A018167 
               A140443
%Y A007053 Adjacent sequences: A007050 A007051 A007052 this_sequence A007054 A007055 
               A007056
%K A007053 nonn,nice
%O A007053 0,3
%A A007053 N. J. A. Sloane (njas(AT)research.att.com), Mira Bernstein, Robert G. 
               Wilson v (rgwv(AT)rgwv.com), S. W. Golomb
%E A007053 More terms from Jud McCranie (j.mccranie(AT)comcast.net)
%E A007053 Extended to n = 52 by Warren D. Smith (wds(AT)research.NJ.NEC.COM), Dec 
               11 2000, computed with Meissel-Lehmer-Legendre inclusion exclusion 
               formula code he wrote back in 1985, recently re-run.