A metadrome is a nonnegative integer whose hexadecimal digits are in strict ascending order. The first few are 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 18, 19, 20, ... (OEIS A023784).
A number whose hexadecimal digits are in nonincreasing order is a nialpdrome. A number can be neither a metadrome nor a nialpdrome, as illustrated by the hexadecimal number 121.
The following table summarizes related classes of numbers.
| name | base-16 digit order |
| katadrome | strict descending |
| metadrome | strict ascending |
| nialpdrome | nonincreasing |
| plaindrome | nondecreasing |
