Number of prime powers (p^2, p^3, ...) <= 2^n.

Terms

a(0) =0a(1) =1a(2) =2a(3) =4a(4) =7a(5) =9a(6) =13a(7) =16a(8) =20a(9) =26a(10) =31a(11) =40a(12) =50a(13) =61a(14) =78a(15) =93a(16) =119a(17) =150a(18) =189a(19) =242a(20) =310a(21) =400a(22) =525a(23) =684a(24) =900a(25) =1190a(26) =1581a(27) =2117a(28) =2836a(29) =3807