The number 21531
21531 is a composite number with 4 divisors. Its prime factorisation is 3 × 7177. Divisors (4): 1, 3, 7177, 21531.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21531: a semiprime: 3 × 7177, the product of two primes.
- 2
21531 is composite. Its prime factorisation is
- 3
The divisors add up to 28712; without 21531 itself that is 7181, so 21531 is deficient (7181 is less than 21531). Euler's totient φ(21531) = 14352 numbers up to 21531 share no factor with it.
- 4
The digits of 21531 add up to 12, and repeating that until one digit is left gives the digital root 3. The Collatz sequence (halve if even, else 3n+1) takes 105 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21531 = 3 \times 7177 \]
21531 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 4 |
| Sum of divisors | 28712 |
| Euler totient φ(n) | 14352 |
| Square | 463583961 |
| Cube | 9981426264291 |
| Square root | 146.734454 |
| Digit sum / digital root | 12 / 3 |
| Collatz steps to 1 | 105 |
| Scientific notation | 2.1531 × |
21531 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand five hundred and thirty-one |
| Binary (base 2) | 101010000011011 |
| Octal (base 8) | 52033 |
| Hexadecimal (base 16) | 541B |
| Base 3 | 1002112110 |
| As time | 21531 seconds = 5 h 58 min 51 s |
Is 21531 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 (21531 ÷ 3 = 7177) | 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 6) | 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 3) | 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 4) | 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 21531 a prime number?
No. 21531 = 3 × 7177, so it is divisible by 3.
What are the factors of 21531?
1, 3, 7177, 21531.
What is 21531 in binary?
101010000011011 (hexadecimal 541B, octal 52033).
What is the square root of 21531?
About 146.7345.
Is 21531 divisible by 3?
Yes. Its digits add up to 12, a multiple of 3.
What is special about the number 21531?
21531 is a semiprime: 3 × 7177, the product of two primes.