21,721 in words
21,721
twenty-one thousand seven hundred and twenty-one
21,721 is written twenty-one thousand seven hundred and twenty-one.
Ways to write it
- As an ordinal
- twenty-one thousand seven hundred and twenty-first
- Expanded form
- 20,000 + 1,000 + 700 + 20 + 1
Place value
| Place | Digit | Value |
|---|---|---|
| ten thousands | 2 | 20,000 |
| thousands | 1 | 1,000 |
| hundreds | 7 | 700 |
| tens | 2 | 20 |
| ones | 1 | 1 |
Number facts
- Even or odd
- Odd
- Prime or composite
- Composite
- Factors
- 1, 7, 29, 107, 203, 749, 3,103 and 21,721 (8 factors)
- First 10 multiples
- 21,721, 43,442, 65,163, 86,884, 108,605, 130,326, 152,047, 173,768, 195,489, 217,210
- Square
- 21,721 × 21,721 = 471,801,841
- Square root
- ≈ 147.38
- Sum of the digits
- 2 + 1 + 7 + 2 + 1 = 13
- Rounded to the nearest 10
- 21,720
- Rounded to the nearest 100
- 21,700
- Rounded to the nearest 1000
- 22,000
- Number before
- 21,720
- Number after
- 21,722
- In binary
101010011011001
Quick check
What number comes just after 21,721?
Show the answer
21,722
Is 21,721 even or odd?
Show the answer
Odd
What is 21,721 + 10?
Show the answer
21,731
Practise with a game
Factors, Multiples & Primes
Multiples, factors, prime numbers, square numbers and prime factors.
Number Patterns
Find the missing number in a sequence.Frequently asked questions
How do you write 21,721 in words?
21,721 is written "twenty-one thousand seven hundred and twenty-one".
Is 21,721 a prime number?
No. 21,721 is a composite number, because it has more than two factors.
What are the factors of 21,721?
The factors of 21,721 are 1, 7, 29, 107, 203, 749, 3,103 and 21,721.