The number 21285
21285 is a composite number with 24 divisors. Its prime factorisation is × 5 × 11 × 43. Divisors (24): 1, 3, 5, 9, 11, 15, 33, 43, 45, 55, 99, 129, 165, 215, 387, 473 … 21285.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
21285 has no famous special property in the usual lists (prime, square, cube, triangular, Fibonacci, palindrome, perfect), but it is still a composite number.
- 2
21285 is composite. Its prime factorisation is
- 3
The divisors add up to 41184; without 21285 itself that is 19899, so 21285 is deficient (19899 is less than 21285). Euler's totient φ(21285) = 10080 numbers up to 21285 share no factor with it.
- 4
The digits of 21285 add up to 18, and repeating that until one digit is left gives the digital root 9. The Collatz sequence (halve if even, else 3n+1) takes 56 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21285 = 3^{2} \times 5 \times 11 \times 43 \]21285 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 24 |
| Sum of divisors | 41184 |
| Euler totient φ(n) | 10080 |
| Square | 453051225 |
| Cube | 9643195324125 |
| Square root | 145.893797 (= 3√2365) |
| Digit sum / digital root | 18 / 9 |
| Collatz steps to 1 | 56 |
| Scientific notation | 2.1285 × |
21285 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand two hundred and eighty-five |
| Binary (base 2) | 101001100100101 |
| Octal (base 8) | 51445 |
| Hexadecimal (base 16) | 5325 |
| Base 3 | 1002012100 |
| As time | 21285 seconds = 5 h 54 min 45 s |
Is 21285 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 (21285 ÷ 3 = 7095) | A number is divisible by 3 if the digits add up to a multiple of 3. |
| 4 | No (remainder 1) | A number is divisible by 4 if the last two digits make a multiple of 4. |
| 5 | Yes (21285 ÷ 5 = 4257) | 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 5) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | Yes (21285 ÷ 9 = 2365) | A number is divisible by 9 if the digits add up to a multiple of 9. |
| 10 | No (remainder 5) | A number is divisible by 10 if the last digit is 0. |
| 11 | Yes (21285 ÷ 11 = 1935) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 9) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 21285 a prime number?
No. 21285 = × 5 × 11 × 43, so it is divisible by 3.
What are the factors of 21285?
1, 3, 5, 9, 11, 15, 33, 43, 45, 55, 99, 129, 165, 215, 387, 473, 495, 645, 1419, 1935, 2365, 4257, 7095, 21285.
What is 21285 in binary?
101001100100101 (hexadecimal 5325, octal 51445).
What is the square root of 21285?
About 145.8938, exactly 3√2365.
Is 21285 divisible by 3?
Yes. Its digits add up to 18, a multiple of 3.
What is special about the number 21285?
It is a composite number with 24 divisors.