Semiprimes in A103380.

Terms

a(0) =4a(1) =9a(2) =15a(3) =21a(4) =33a(5) =38a(6) =58a(7) =65a(8) =86a(9) =106a(10) =121a(11) =129a(12) =265a(13) =511a(14) =2047a(15) =2049a(16) =4097a(17) =4109a(18) =8193a(19) =17855a(20) =19857a(21) =34709a(22) =66233a(23) =104739a(24) =130953a(25) =131209a(26) =140474a(27) =220918a(28) =258931a(29) =511673