The number 21724
21724 is a composite number with 6 divisors. Its prime factorisation is × 5431. Divisors (6): 1, 2, 4, 5431, 10862, 21724.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
21724 has no famous special property in the usual lists (prime, square, cube, triangular, Fibonacci, palindrome, perfect), but it is still a composite number.
- 2
21724 is composite. Its prime factorisation is
- 3
The divisors add up to 38024; without 21724 itself that is 16300, so 21724 is deficient (16300 is less than 21724). Euler's totient φ(21724) = 10860 numbers up to 21724 share no factor with it.
- 4
The digits of 21724 add up to 16, and repeating that until one digit is left gives the digital root 7. The Collatz sequence (halve if even, else 3n+1) takes 100 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21724 = 2^{2} \times 5431 \]21724 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 6 |
| Sum of divisors | 38024 |
| Euler totient φ(n) | 10860 |
| Square | 471932176 |
| Cube | 10252254591424 |
| Square root | 147.390637 (= 2√5431) |
| Digit sum / digital root | 16 / 7 |
| Collatz steps to 1 | 100 |
| Scientific notation | 2.1724 × |
21724 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand seven hundred and twenty-four |
| Binary (base 2) | 101010011011100 |
| Octal (base 8) | 52334 |
| Hexadecimal (base 16) | 54DC |
| Base 3 | 1002210121 |
| As time | 21724 seconds = 6 h 2 min 4 s |
Is 21724 divisible by 2 to 12?
| Divisor | Answer | Rule |
|---|---|---|
| 2 | Yes (21724 ÷ 2 = 10862) | A number is divisible by 2 if the last digit is even (0, 2, 4, 6, 8). |
| 3 | No (remainder 1) | A number is divisible by 3 if the digits add up to a multiple of 3. |
| 4 | Yes (21724 ÷ 4 = 5431) | A number is divisible by 4 if the last two digits make a multiple of 4. |
| 5 | No (remainder 4) | A number is divisible by 5 if the last digit is 0 or 5. |
| 6 | No (remainder 4) | A number is divisible by 6 if it is divisible by both 2 and 3. |
| 7 | No (remainder 3) | A number is divisible by 7 if double the last digit and subtract it from the rest: the result is a multiple of 7. |
| 8 | No (remainder 4) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | No (remainder 7) | A number is divisible by 9 if the digits add up to a multiple of 9. |
| 10 | No (remainder 4) | A number is divisible by 10 if the last digit is 0. |
| 11 | No (remainder 10) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 4) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 21724 a prime number?
No. 21724 = × 5431, so it is divisible by 2.
What are the factors of 21724?
1, 2, 4, 5431, 10862, 21724.
What is 21724 in binary?
101010011011100 (hexadecimal 54DC, octal 52334).
What is the square root of 21724?
About 147.3906, exactly 2√5431.
Is 21724 divisible by 3?
No. Its digits add up to 16, which is not a multiple of 3.
What is special about the number 21724?
It is a composite number with 6 divisors.