Numbers k such that (k*2^d - 1)*(d*2^k - 1) is semiprime for some divisor d of k.

Terms

a(0) =2a(1) =3a(2) =6a(3) =7a(4) =12a(5) =18a(6) =19a(7) =21a(8) =30a(9) =31a(10) =42a(11) =60a(12) =75a(13) =81a(14) =115a(15) =123a(16) =126a(17) =132a(18) =133a(19) =225a(20) =249a(21) =306a(22) =324a(23) =362a(24) =384a(25) =462a(26) =468a(27) =512a(28) =606a(29) =607