Katadromes: digits in base 15 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) =10a(11) =11a(12) =12a(13) =13a(14) =14a(15) =15a(16) =30a(17) =31a(18) =45a(19) =46a(20) =47a(21) =60a(22) =61a(23) =62a(24) =63a(25) =75a(26) =76a(27) =77a(28) =78a(29) =79