Katadromes: digits in base 9 are in strict descending order.

Terms

a(0) =0a(1) =1a(2) =2a(3) =3a(4) =4a(5) =5a(6) =6a(7) =7a(8) =8a(9) =9a(10) =18a(11) =19a(12) =27a(13) =28a(14) =29a(15) =36a(16) =37a(17) =38a(18) =39a(19) =45a(20) =46a(21) =47a(22) =48a(23) =49a(24) =54a(25) =55a(26) =56a(27) =57a(28) =58a(29) =59