21 Decimal to Roman numerals
21 decimal = XXI Roman numerals
21 written in Roman numerals is XXI.
21 decimal = XXI Roman numerals
How to convert 21 to Roman numerals
Decimal to Roman numerals
Take away the largest Roman value that fits, write its symbol, and repeat until nothing is left:
| Remaining | Take away | Write |
|---|---|---|
| 21 | 10 | X |
| 11 | 10 | X |
| 1 | 1 | I |
Result: 21 = XXI in Roman numerals.
21 (decimal) in other systems
| Binary | 10101 |
| Hexadecimal | 15 |
| Octal | 25 |
| Duodecimal | 19 |
| Ternary | 210 |
| Base 36 | L |
| Vigesimal | 11 |
| Quaternary | 111 |
| Quinary | 41 |
| Senary | 33 |
Nearby decimal to Roman numerals conversions
About the number 21
- 21 is an odd number.
- 21 is not a prime number.
- Written in binary it needs 5 bits, so it fits in one byte.
Reverse conversion
Frequently asked questions
What is 21 in Roman numerals?
21 in decimal is XXI in Roman numerals.