a(n) = prime(2^n) + 1.

Terms

a(0) =3a(1) =4a(2) =8a(3) =20a(4) =54a(5) =132a(6) =312a(7) =720a(8) =1620a(9) =3672a(10) =8162a(11) =17864a(12) =38874a(13) =84018a(14) =180504a(15) =386094a(16) =821642a(17) =1742538a(18) =3681132a(19) =7754078a(20) =16290048a(21) =34136030a(22) =71378570a(23) =148948140a(24) =310248242a(25) =645155198a(26) =1339484198a(27) =2777105130a(28) =5750079048a(29) =11891268402