Number of primes <= 2^n.

Terms

a(0) =0a(1) =1a(2) =2a(3) =4a(4) =6a(5) =11a(6) =18a(7) =31a(8) =54a(9) =97a(10) =172a(11) =309a(12) =564a(13) =1028a(14) =1900a(15) =3512a(16) =6542a(17) =12251a(18) =23000a(19) =43390a(20) =82025a(21) =155611a(22) =295947a(23) =564163a(24) =1077871a(25) =2063689a(26) =3957809a(27) =7603553a(28) =14630843a(29) =28192750