The number 21385
21385 is a composite number with 16 divisors. Its prime factorisation is 5 × 7 × 13 × 47. Divisors (16): 1, 5, 7, 13, 35, 47, 65, 91, 235, 329, 455, 611, 1645, 3055, 4277, 21385.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21385: a happy number: repeatedly adding the squares of its digits reaches 1.
- 2
21385 is composite. Its prime factorisation is
- 3
The divisors add up to 32256; without 21385 itself that is 10871, so 21385 is deficient (10871 is less than 21385). Euler's totient φ(21385) = 13248 numbers up to 21385 share no factor with it.
- 4
The digits of 21385 add up to 19, and repeating that until one digit is left gives the digital root 1. The Collatz sequence (halve if even, else 3n+1) takes 100 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21385 = 5 \times 7 \times 13 \times 47 \]
21385 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 16 |
| Sum of divisors | 32256 |
| Euler totient φ(n) | 13248 |
| Square | 457318225 |
| Cube | 9779750241625 |
| Square root | 146.236110 |
| Digit sum / digital root | 19 / 1 |
| Collatz steps to 1 | 100 |
| Scientific notation | 2.1385 × |
21385 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand three hundred and eighty-five |
| Binary (base 2) | 101001110001001 |
| Octal (base 8) | 51611 |
| Hexadecimal (base 16) | 5389 |
| Base 3 | 1002100001 |
| As time | 21385 seconds = 5 h 56 min 25 s |
Is 21385 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 | No (remainder 1) | 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 (21385 ÷ 5 = 4277) | A number is divisible by 5 if the last digit is 0 or 5. |
| 6 | No (remainder 1) | A number is divisible by 6 if it is divisible by both 2 and 3. |
| 7 | Yes (21385 ÷ 7 = 3055) | 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 1) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | No (remainder 1) | 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 | No (remainder 1) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 1) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 21385 a prime number?
No. 21385 = 5 × 7 × 13 × 47, so it is divisible by 5.
What are the factors of 21385?
1, 5, 7, 13, 35, 47, 65, 91, 235, 329, 455, 611, 1645, 3055, 4277, 21385.
What is 21385 in binary?
101001110001001 (hexadecimal 5389, octal 51611).
What is the square root of 21385?
About 146.2361.
Is 21385 divisible by 3?
No. Its digits add up to 19, which is not a multiple of 3.
What is special about the number 21385?
21385 is a happy number: repeatedly adding the squares of its digits reaches 1.