The number 31721
31721 is a twin prime (31721 and 31723 are both prime) and the 3410th prime number. Its only divisors are 1 and 31721.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 31721: a twin prime (31721 and 31723 are both prime); the 3410th prime number.
- 2
31721 is prime, so its only factors are 1 and 31721. It is the 3410th prime; the next prime is 31723 and the one before is 31699.
- 3
The divisors add up to 31722; without 31721 itself that is 1, so 31721 is deficient (1 is less than 31721). Euler's totient φ(31721) = 31720 numbers up to 31721 share no factor with it.
- 4
The digits of 31721 add up to 14, and repeating that until one digit is left gives the digital root 5. The Collatz sequence (halve if even, else 3n+1) takes 129 steps to reach 1.
31721 at a glance
| Property | Value |
|---|---|
| Type | prime |
| Number of divisors | 2 |
| Sum of divisors | 31722 |
| Euler totient φ(n) | 31720 |
| Square | 1006221841 |
| Cube | 31918363018361 |
| Square root | 178.103902 |
| Digit sum / digital root | 14 / 5 |
| Collatz steps to 1 | 129 |
| Scientific notation | 3.1721 × |
31721 in other forms
| Form | Value |
|---|---|
| In words | thirty-one thousand seven hundred and twenty-one |
| Binary (base 2) | 111101111101001 |
| Octal (base 8) | 75751 |
| Hexadecimal (base 16) | 7BE9 |
| Base 3 | 1121111212 |
| As time | 31721 seconds = 8 h 48 min 41 s |
Is 31721 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 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 5) | A number is divisible by 6 if it is divisible by both 2 and 3. |
| 7 | No (remainder 4) | 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 5) | 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 5) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 31721 a prime number?
Yes. 31721 is divisible only by 1 and itself.
What are the factors of 31721?
1, 31721.
What is 31721 in binary?
111101111101001 (hexadecimal 7BE9, octal 75751).
What is the square root of 31721?
About 178.1039.
Is 31721 divisible by 3?
No. Its digits add up to 14, which is not a multiple of 3.
What is special about the number 31721?
31721 is a twin prime (31721 and 31723 are both prime); the 3410th prime number.