The number 21831
21831 is a composite number with 8 divisors. Its prime factorisation is 3 × 19 × 383. Divisors (8): 1, 3, 19, 57, 383, 1149, 7277, 21831.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21831: a happy number: repeatedly adding the squares of its digits reaches 1.
- 2
21831 is composite. Its prime factorisation is
- 3
The divisors add up to 30720; without 21831 itself that is 8889, so 21831 is deficient (8889 is less than 21831). Euler's totient φ(21831) = 13752 numbers up to 21831 share no factor with it.
- 4
The digits of 21831 add up to 15, and repeating that until one digit is left gives the digital root 6. The Collatz sequence (halve if even, else 3n+1) takes 74 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21831 = 3 \times 19 \times 383 \]
21831 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 8 |
| Sum of divisors | 30720 |
| Euler totient φ(n) | 13752 |
| Square | 476592561 |
| Cube | 10404492199191 |
| Square root | 147.753173 |
| Digit sum / digital root | 15 / 6 |
| Collatz steps to 1 | 74 |
| Scientific notation | 2.1831 × |
21831 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand eight hundred and thirty-one |
| Binary (base 2) | 101010101000111 |
| Octal (base 8) | 52507 |
| Hexadecimal (base 16) | 5547 |
| Base 3 | 1002221120 |
| As time | 21831 seconds = 6 h 3 min 51 s |
Is 21831 divisible by 2 to 12?
| Divisor | Answer | Rule |
|---|---|---|
| 2 | No (remainder 1) | A number is divisible by 2 if the last digit is even (0, 2, 4, 6, 8). |
| 3 | Yes (21831 ÷ 3 = 7277) | A number is divisible by 3 if the digits add up to a multiple of 3. |
| 4 | No (remainder 3) | A number is divisible by 4 if the last two digits make a multiple of 4. |
| 5 | No (remainder 1) | A number is divisible by 5 if the last digit is 0 or 5. |
| 6 | No (remainder 3) | A number is divisible by 6 if it is divisible by both 2 and 3. |
| 7 | No (remainder 5) | 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 7) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | No (remainder 6) | A number is divisible by 9 if the digits add up to a multiple of 9. |
| 10 | No (remainder 1) | A number is divisible by 10 if the last digit is 0. |
| 11 | No (remainder 7) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 3) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 21831 a prime number?
No. 21831 = 3 × 19 × 383, so it is divisible by 3.
What are the factors of 21831?
1, 3, 19, 57, 383, 1149, 7277, 21831.
What is 21831 in binary?
101010101000111 (hexadecimal 5547, octal 52507).
What is the square root of 21831?
About 147.7532.
Is 21831 divisible by 3?
Yes. Its digits add up to 15, a multiple of 3.
What is special about the number 21831?
21831 is a happy number: repeatedly adding the squares of its digits reaches 1.