The number 21397
21397 is the 2402nd prime number. Its only divisors are 1 and 21397.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21397: the 2402nd prime number.
- 2
21397 is prime, so its only factors are 1 and 21397. It is the 2402nd prime; the next prime is 21401 and the one before is 21391.
- 3
The divisors add up to 21398; without 21397 itself that is 1, so 21397 is deficient (1 is less than 21397). Euler's totient φ(21397) = 21396 numbers up to 21397 share no factor with it.
- 4
The digits of 21397 add up to 22, and repeating that until one digit is left gives the digital root 4. The Collatz sequence (halve if even, else 3n+1) takes 48 steps to reach 1.
21397 at a glance
| Property | Value |
|---|---|
| Type | prime |
| Number of divisors | 2 |
| Sum of divisors | 21398 |
| Euler totient φ(n) | 21396 |
| Square | 457831609 |
| Cube | 9796222937773 |
| Square root | 146.277134 |
| Digit sum / digital root | 22 / 4 |
| Collatz steps to 1 | 48 |
| Scientific notation | 2.1397 × |
21397 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand three hundred and ninety-seven |
| Binary (base 2) | 101001110010101 |
| Octal (base 8) | 51625 |
| Hexadecimal (base 16) | 5395 |
| Base 3 | 1002100111 |
| As time | 21397 seconds = 5 h 56 min 37 s |
Is 21397 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 | No (remainder 2) | 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 | 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 | No (remainder 4) | 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 2) | 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 21397 a prime number?
Yes. 21397 is divisible only by 1 and itself.
What are the factors of 21397?
1, 21397.
What is 21397 in binary?
101001110010101 (hexadecimal 5395, octal 51625).
What is the square root of 21397?
About 146.2771.
Is 21397 divisible by 3?
No. Its digits add up to 22, which is not a multiple of 3.
What is special about the number 21397?
21397 is the 2402nd prime number.