| Factorisation | 2 × 13 × 823 |
| Prime | no |
| Binary | 101001110010110 |
| Hexadecimal | 0x5396 |
| Bit length | 15 |
| Digit sum | 23 |
| Digits spoken | two one three nine eight |
21398 opens the sequence 2139847, beginning at digit 1 of seven.
21398 falls below the cardinality of a PubMed record, a Canadian patent application, a European patent application. Those systems assign identifiers sequentially, so it necessarily holds one in each. This is a property of the registries, not of the number. The cardinalities are published here.