a(n) is the least prime p such that p-1 is divisible by 2^n and not by 2^(n+1).

Terms

a(0) =2a(1) =3a(2) =5a(3) =41a(4) =17a(5) =97a(6) =193a(7) =641a(8) =257a(9) =7681a(10) =13313a(11) =18433a(12) =12289a(13) =40961a(14) =114689a(15) =163841a(16) =65537a(17) =1179649a(18) =786433a(19) =5767169a(20) =7340033a(21) =23068673a(22) =104857601a(23) =377487361a(24) =754974721a(25) =167772161a(26) =469762049a(27) =2013265921a(28) =3489660929a(29) =12348030977