Number of primes < 2^prime(n).

Terms

a(0) =2a(1) =4a(2) =11a(3) =31a(4) =309a(5) =1028a(6) =12251a(7) =43390a(8) =564163a(9) =28192750a(10) =105097565a(11) =5586502348a(12) =80316571436a(13) =305761713237