Numbers k such that 2^k + 1 is a semiprime.

Terms

a(0) =3a(1) =5a(2) =6a(3) =7a(4) =11a(5) =12a(6) =13a(7) =17a(8) =19a(9) =20a(10) =23a(11) =28a(12) =31a(13) =32a(14) =40a(15) =43a(16) =61a(17) =64a(18) =79a(19) =92a(20) =101a(21) =104a(22) =127a(23) =128a(24) =148a(25) =167a(26) =191a(27) =199a(28) =256a(29) =313