The number 31391
31391 is a twin prime (31391 and 31393 are both prime) and the 3383rd prime number. Its only divisors are 1 and 31391.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 31391: a twin prime (31391 and 31393 are both prime); the 3383rd prime number.
- 2
31391 is prime, so its only factors are 1 and 31391. It is the 3383rd prime; the next prime is 31393 and the one before is 31387.
- 3
The divisors add up to 31392; without 31391 itself that is 1, so 31391 is deficient (1 is less than 31391). Euler's totient φ(31391) = 31390 numbers up to 31391 share no factor with it.
- 4
The digits of 31391 add up to 17, and repeating that until one digit is left gives the digital root 8. The Collatz sequence (halve if even, else 3n+1) takes 85 steps to reach 1.
31391 at a glance
| Property | Value |
|---|---|
| Type | prime |
| Number of divisors | 2 |
| Sum of divisors | 31392 |
| Euler totient φ(n) | 31390 |
| Square | 985394881 |
| Cube | 30932530709471 |
| Square root | 177.175055 |
| Digit sum / digital root | 17 / 8 |
| Collatz steps to 1 | 85 |
| Scientific notation | 3.1391 × |
31391 in other forms
| Form | Value |
|---|---|
| In words | thirty-one thousand three hundred and ninety-one |
| Binary (base 2) | 111101010011111 |
| Octal (base 8) | 75237 |
| Hexadecimal (base 16) | 7A9F |
| Base 3 | 1121001122 |
| As time | 31391 seconds = 8 h 43 min 11 s |
Is 31391 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 2) | 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 1) | A number is divisible by 5 if the last digit is 0 or 5. |
| 6 | No (remainder 5) | 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 | No (remainder 8) | A number is divisible by 9 if the digits add up to a multiple of 9. |
| 10 | No (remainder 1) | A number is divisible by 10 if the last digit is 0. |
| 11 | No (remainder 8) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 11) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 31391 a prime number?
Yes. 31391 is divisible only by 1 and itself.
What are the factors of 31391?
1, 31391.
What is 31391 in binary?
111101010011111 (hexadecimal 7A9F, octal 75237).
What is the square root of 31391?
About 177.1751.
Is 31391 divisible by 3?
No. Its digits add up to 17, which is not a multiple of 3.
What is special about the number 31391?
31391 is a twin prime (31391 and 31393 are both prime); the 3383rd prime number.