Wagstaff numbers: numbers k such that (2^k + 1)/3 is prime.

Terms

a(0) =3a(1) =5a(2) =7a(3) =11a(4) =13a(5) =17a(6) =19a(7) =23a(8) =31a(9) =43a(10) =61a(11) =79a(12) =101a(13) =127a(14) =167a(15) =191a(16) =199a(17) =313a(18) =347a(19) =701a(20) =1709a(21) =2617a(22) =3539a(23) =5807a(24) =10501a(25) =10691a(26) =11279a(27) =12391a(28) =14479a(29) =42737