The number 251
251 is the 54th prime number. Its only divisors are 1 and 251.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 251: the 54th prime number.
- 2
251 is prime, so its only factors are 1 and 251. It is the 54th prime; the next prime is 257 and the one before is 241.
- 3
The divisors add up to 252; without 251 itself that is 1, so 251 is deficient (1 is less than 251). Euler's totient φ(251) = 250 numbers up to 251 share no factor with it.
- 4
The digits of 251 add up to 8, and repeating that until one digit is left gives the digital root 8. The Collatz sequence (halve if even, else 3n+1) takes 65 steps to reach 1.
251 at a glance
| Property | Value |
|---|---|
| Type | prime |
| Number of divisors | 2 |
| Sum of divisors | 252 |
| Euler totient φ(n) | 250 |
| Square | 63001 |
| Cube | 15813251 |
| Square root | 15.842980 |
| Digit sum / digital root | 8 / 8 |
| Collatz steps to 1 | 65 |
| Scientific notation | 2.51 × |
251 in other forms
| Form | Value |
|---|---|
| In words | two hundred and fifty-one |
| Roman numerals | CCLI |
| Binary (base 2) | 11111011 |
| Octal (base 8) | 373 |
| Hexadecimal (base 16) | FB |
| Base 3 | 100022 |
| As time | 251 seconds = 4 min 11 s |
Is 251 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 6) | 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 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 9) | 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 251 a prime number?
Yes. 251 is divisible only by 1 and itself.
What are the factors of 251?
1, 251.
What is 251 in binary?
11111011 (hexadecimal FB, octal 373).
What is the square root of 251?
About 15.8430.
What is 251 in Roman numerals?
CCLI.
Is 251 divisible by 3?
No. Its digits add up to 8, which is not a multiple of 3.
What is special about the number 251?
251 is the 54th prime number.