Numbers k such that 2^k + 1 has just two distinct prime factors.

Terms

a(0) =5a(1) =6a(2) =7a(3) =9a(4) =10a(5) =11a(6) =12a(7) =13a(8) =17a(9) =19a(10) =20a(11) =23a(12) =28a(13) =31a(14) =32a(15) =40a(16) =43a(17) =61a(18) =64a(19) =79a(20) =92a(21) =101a(22) =104a(23) =127a(24) =128a(25) =148a(26) =167a(27) =191a(28) =199a(29) =256