The number 31981
31981 is the 3431st prime number. Its only divisors are 1 and 31981.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 31981: the 3431st prime number.
- 2
31981 is prime, so its only factors are 1 and 31981. It is the 3431st prime; the next prime is 31991 and the one before is 31973.
- 3
The divisors add up to 31982; without 31981 itself that is 1, so 31981 is deficient (1 is less than 31981). Euler's totient φ(31981) = 31980 numbers up to 31981 share no factor with it.
- 4
The digits of 31981 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 54 steps to reach 1.
31981 at a glance
| Property | Value |
|---|---|
| Type | prime |
| Number of divisors | 2 |
| Sum of divisors | 31982 |
| Euler totient φ(n) | 31980 |
| Square | 1022784361 |
| Cube | 32709666649141 |
| Square root | 178.832324 |
| Digit sum / digital root | 22 / 4 |
| Collatz steps to 1 | 54 |
| Scientific notation | 3.1981 × |
31981 in other forms
| Form | Value |
|---|---|
| In words | thirty-one thousand nine hundred and eighty-one |
| Binary (base 2) | 111110011101101 |
| Octal (base 8) | 76355 |
| Hexadecimal (base 16) | 7CED |
| Base 3 | 1121212111 |
| As time | 31981 seconds = 8 h 53 min 1 s |
Is 31981 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 1) | 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 1) | A number is divisible by 10 if the last digit is 0. |
| 11 | No (remainder 4) | 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 31981 a prime number?
Yes. 31981 is divisible only by 1 and itself.
What are the factors of 31981?
1, 31981.
What is 31981 in binary?
111110011101101 (hexadecimal 7CED, octal 76355).
What is the square root of 31981?
About 178.8323.
Is 31981 divisible by 3?
No. Its digits add up to 22, which is not a multiple of 3.
What is special about the number 31981?
31981 is the 3431st prime number.