A katadrome is a number whose hexadecimal digits are in strict descending order. The first few are 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 32, 33, 48, 49, ... (OEIS A023797), corresponding to 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, F, 10, 20, 21, 30, 31, ....
A number that is not a katadrome is a plaindrome.
The following table summarized related classes of numbers.
| name | base-16 digit order |
| katadrome | strict descending |
| metadrome | strict ascending |
| nialpdrome | nonincreasing |
| plaindrome | nondecreasing |
