Binary encoding of semiprimes (A001358).

Terms

a(0) =2a(1) =3a(2) =4a(3) =5a(4) =9a(5) =6a(6) =10a(7) =17a(8) =8a(9) =33a(10) =18a(11) =65a(12) =12a(13) =129a(14) =34a(15) =257a(16) =16a(17) =66a(18) =20a(19) =130a(20) =513a(21) =1025a(22) =36a(23) =258a(24) =2049a(25) =24a(26) =4097a(27) =68a(28) =8193a(29) =514