Semiprimes that contain only digits 4 and 9.

Terms

a(0) =4a(1) =9a(2) =49a(3) =94a(4) =949a(5) =4449a(6) =4499a(7) =9449a(8) =44494a(9) =44949a(10) =44999a(11) =49949a(12) =94499a(13) =94994a(14) =99449a(15) =99494a(16) =99949a(17) =444494a(18) =444949a(19) =494449a(20) =494999a(21) =499949a(22) =944494a(23) =944949a(24) =944999a(25) =949999a(26) =994999a(27) =999494a(28) =4444449a(29) =4444499