The number 21731
21731 is a composite number with 4 divisors. Its prime factorisation is 31 × 701. Divisors (4): 1, 31, 701, 21731.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21731: a semiprime: 31 × 701, the product of two primes.
- 2
21731 is composite. Its prime factorisation is
- 3
The divisors add up to 22464; without 21731 itself that is 733, so 21731 is deficient (733 is less than 21731). Euler's totient φ(21731) = 21000 numbers up to 21731 share no factor with it.
- 4
The digits of 21731 add up to 14, and repeating that until one digit is left gives the digital root 5. The Collatz sequence (halve if even, else 3n+1) takes 56 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21731 = 31 \times 701 \]
21731 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 4 |
| Sum of divisors | 22464 |
| Euler totient φ(n) | 21000 |
| Square | 472236361 |
| Cube | 10262168360891 |
| Square root | 147.414382 |
| Digit sum / digital root | 14 / 5 |
| Collatz steps to 1 | 56 |
| Scientific notation | 2.1731 × |
21731 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand seven hundred and thirty-one |
| Binary (base 2) | 101010011100011 |
| Octal (base 8) | 52343 |
| Hexadecimal (base 16) | 54E3 |
| Base 3 | 1002210212 |
| As time | 21731 seconds = 6 h 2 min 11 s |
Is 21731 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 | No (remainder 2) | 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 5) | 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 3) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | No (remainder 5) | 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 6) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 11) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 21731 a prime number?
No. 21731 = 31 × 701, so it is divisible by 31.
What are the factors of 21731?
1, 31, 701, 21731.
What is 21731 in binary?
101010011100011 (hexadecimal 54E3, octal 52343).
What is the square root of 21731?
About 147.4144.
Is 21731 divisible by 3?
No. Its digits add up to 14, which is not a multiple of 3.
What is special about the number 21731?
21731 is a semiprime: 31 × 701, the product of two primes.