The number 21087
21087 is a composite number with 16 divisors. Its prime factorisation is × 11 × 71. Divisors (16): 1, 3, 9, 11, 27, 33, 71, 99, 213, 297, 639, 781, 1917, 2343, 7029, 21087.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
21087 has no famous special property in the usual lists (prime, square, cube, triangular, Fibonacci, palindrome, perfect), but it is still a composite number.
- 2
21087 is composite. Its prime factorisation is
- 3
The divisors add up to 34560; without 21087 itself that is 13473, so 21087 is deficient (13473 is less than 21087). Euler's totient φ(21087) = 12600 numbers up to 21087 share no factor with it.
- 4
The digits of 21087 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 180 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21087 = 3^{3} \times 11 \times 71 \]21087 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 16 |
| Sum of divisors | 34560 |
| Euler totient φ(n) | 12600 |
| Square | 444661569 |
| Cube | 9376578505503 |
| Square root | 145.213636 (= 3√2343) |
| Digit sum / digital root | 18 / 9 |
| Collatz steps to 1 | 180 |
| Scientific notation | 2.1087 × |
21087 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand and eighty-seven |
| Binary (base 2) | 101001001011111 |
| Octal (base 8) | 51137 |
| Hexadecimal (base 16) | 525F |
| Base 3 | 1001221000 |
| As time | 21087 seconds = 5 h 51 min 27 s |
Is 21087 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 (21087 ÷ 3 = 7029) | 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 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 7) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | Yes (21087 ÷ 9 = 2343) | 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 | Yes (21087 ÷ 11 = 1917) | 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 21087 a prime number?
No. 21087 = × 11 × 71, so it is divisible by 3.
What are the factors of 21087?
1, 3, 9, 11, 27, 33, 71, 99, 213, 297, 639, 781, 1917, 2343, 7029, 21087.
What is 21087 in binary?
101001001011111 (hexadecimal 525F, octal 51137).
What is the square root of 21087?
About 145.2136, exactly 3√2343.
Is 21087 divisible by 3?
Yes. Its digits add up to 18, a multiple of 3.
What is special about the number 21087?
It is a composite number with 16 divisors.