Numbers with digits 6 and 9 only.

Terms

a(0) =6a(1) =9a(2) =66a(3) =69a(4) =96a(5) =99a(6) =666a(7) =669a(8) =696a(9) =699a(10) =966a(11) =969a(12) =996a(13) =999a(14) =6666a(15) =6669a(16) =6696a(17) =6699a(18) =6966a(19) =6969a(20) =6996a(21) =6999a(22) =9666a(23) =9669a(24) =9696a(25) =9699a(26) =9966a(27) =9969a(28) =9996a(29) =9999