a(n) = prime(2^n).

Terms

a(0) =2a(1) =3a(2) =7a(3) =19a(4) =53a(5) =131a(6) =311a(7) =719a(8) =1619a(9) =3671a(10) =8161a(11) =17863a(12) =38873a(13) =84017a(14) =180503a(15) =386093a(16) =821641a(17) =1742537a(18) =3681131a(19) =7754077a(20) =16290047a(21) =34136029a(22) =71378569a(23) =148948139a(24) =310248241a(25) =645155197a(26) =1339484197a(27) =2777105129a(28) =5750079047a(29) =11891268401