The number 21687
21687 is a composite number with 4 divisors. Its prime factorisation is 3 × 7229. Divisors (4): 1, 3, 7229, 21687.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21687: a semiprime: 3 × 7229, the product of two primes.
- 2
21687 is composite. Its prime factorisation is
- 3
The divisors add up to 28920; without 21687 itself that is 7233, so 21687 is deficient (7233 is less than 21687). Euler's totient φ(21687) = 14456 numbers up to 21687 share no factor with it.
- 4
The digits of 21687 add up to 24, and repeating that until one digit is left gives the digital root 6. The Collatz sequence (halve if even, else 3n+1) takes 162 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21687 = 3 \times 7229 \]
21687 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 4 |
| Sum of divisors | 28920 |
| Euler totient φ(n) | 14456 |
| Square | 470325969 |
| Cube | 10199959289703 |
| Square root | 147.265067 |
| Digit sum / digital root | 24 / 6 |
| Collatz steps to 1 | 162 |
| Scientific notation | 2.1687 × |
21687 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand six hundred and eighty-seven |
| Binary (base 2) | 101010010110111 |
| Octal (base 8) | 52267 |
| Hexadecimal (base 16) | 54B7 |
| Base 3 | 1002202020 |
| As time | 21687 seconds = 6 h 1 min 27 s |
Is 21687 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 (21687 ÷ 3 = 7229) | 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 2) | 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 1) | 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 7) | 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 3) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 21687 a prime number?
No. 21687 = 3 × 7229, so it is divisible by 3.
What are the factors of 21687?
1, 3, 7229, 21687.
What is 21687 in binary?
101010010110111 (hexadecimal 54B7, octal 52267).
What is the square root of 21687?
About 147.2651.
Is 21687 divisible by 3?
Yes. Its digits add up to 24, a multiple of 3.
What is special about the number 21687?
21687 is a semiprime: 3 × 7229, the product of two primes.