21 in Roman Numerals
XXI
21 in Roman numerals is XXI, and is spelled twenty-one.
How to write 21 in Roman numerals
To write 21 in Roman numerals, combine XX (20) and I (1) to get XXI.
The numeral XXI is read from left to right, from the largest value to the smallest, adding each symbol as you go.
| Value | Roman |
|---|---|
| 20 | XX |
| 1 | I |
| 21 | XXI |
Facts about the number 21
- 21 is an odd number.
- 21 is a composite number. Its prime factorization is 3 × 7.
- The digits of 21 add up to 3.
- 21 has 4 divisors.
21 in other number systems
| Decimal | 21 |
| Roman | XXI |
| Binary | 10101 |
| Octal | 25 |
| Hexadecimal | 15 |
Frequently asked questions
How do you write 21 in Roman numerals?
21 is written as XXI in Roman numerals.
What does the Roman numeral XXI mean?
XXI represents the number 21 (twenty-one).
Is 21 a prime number?
No, 21 is a composite number.
What is 21 in binary and hexadecimal?
21 is 10101 in binary and 15 in hexadecimal.
Related numbers
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