The number 21387
21387 is a composite number with 4 divisors. Its prime factorisation is 3 × 7129. Divisors (4): 1, 3, 7129, 21387.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21387: a semiprime: 3 × 7129, the product of two primes.
- 2
21387 is composite. Its prime factorisation is
- 3
The divisors add up to 28520; without 21387 itself that is 7133, so 21387 is deficient (7133 is less than 21387). Euler's totient φ(21387) = 14256 numbers up to 21387 share no factor with it.
- 4
The digits of 21387 add up to 21, and repeating that until one digit is left gives the digital root 3. The Collatz sequence (halve if even, else 3n+1) takes 162 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21387 = 3 \times 7129 \]
21387 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 4 |
| Sum of divisors | 28520 |
| Euler totient φ(n) | 14256 |
| Square | 457403769 |
| Cube | 9782494407603 |
| Square root | 146.242949 |
| Digit sum / digital root | 21 / 3 |
| Collatz steps to 1 | 162 |
| Scientific notation | 2.1387 × |
21387 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand three hundred and eighty-seven |
| Binary (base 2) | 101001110001011 |
| Octal (base 8) | 51613 |
| Hexadecimal (base 16) | 538B |
| Base 3 | 1002100010 |
| As time | 21387 seconds = 5 h 56 min 27 s |
Is 21387 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 (21387 ÷ 3 = 7129) | 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 2) | 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 7) | A number is divisible by 10 if the last digit is 0. |
| 11 | No (remainder 3) | 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 21387 a prime number?
No. 21387 = 3 × 7129, so it is divisible by 3.
What are the factors of 21387?
1, 3, 7129, 21387.
What is 21387 in binary?
101001110001011 (hexadecimal 538B, octal 51613).
What is the square root of 21387?
About 146.2429.
Is 21387 divisible by 3?
Yes. Its digits add up to 21, a multiple of 3.
What is special about the number 21387?
21387 is a semiprime: 3 × 7129, the product of two primes.