Number of primes less than 2^n.

Terms

a(0) =0a(1) =2a(2) =4a(3) =6a(4) =11a(5) =18a(6) =31a(7) =54a(8) =97a(9) =172a(10) =309a(11) =564a(12) =1028a(13) =1900a(14) =3512a(15) =6542a(16) =12251a(17) =23000a(18) =43390a(19) =82025a(20) =155611a(21) =295947a(22) =564163a(23) =1077871a(24) =2063689a(25) =3957809a(26) =7603553a(27) =14630843a(28) =28192750a(29) =54400028