The number 491
491 is the 94th prime number. Its only divisors are 1 and 491.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 491: the 94th prime number.
- 2
491 is prime, so its only factors are 1 and 491. It is the 94th prime; the next prime is 499 and the one before is 487.
- 3
The divisors add up to 492; without 491 itself that is 1, so 491 is deficient (1 is less than 491). Euler's totient φ(491) = 490 numbers up to 491 share no factor with it.
- 4
The digits of 491 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 141 steps to reach 1.
491 at a glance
| Property | Value |
|---|---|
| Type | prime |
| Number of divisors | 2 |
| Sum of divisors | 492 |
| Euler totient φ(n) | 490 |
| Square | 241081 |
| Cube | 118370771 |
| Square root | 22.158520 |
| Digit sum / digital root | 14 / 5 |
| Collatz steps to 1 | 141 |
| Scientific notation | 4.91 × |
491 in other forms
| Form | Value |
|---|---|
| In words | four hundred and ninety-one |
| Roman numerals | CDXCI |
| Binary (base 2) | 111101011 |
| Octal (base 8) | 753 |
| Hexadecimal (base 16) | 1EB |
| Base 3 | 200012 |
| As time | 491 seconds = 8 min 11 s |
Is 491 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 1) | 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 3) | 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 7) | 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 491 a prime number?
Yes. 491 is divisible only by 1 and itself.
What are the factors of 491?
1, 491.
What is 491 in binary?
111101011 (hexadecimal 1EB, octal 753).
What is the square root of 491?
About 22.1585.
What is 491 in Roman numerals?
CDXCI.
Is 491 divisible by 3?
No. Its digits add up to 14, which is not a multiple of 3.
What is special about the number 491?
491 is the 94th prime number.