The number 643
643 is a twin prime (641 and 643 are both prime) and the 117th prime number. Its only divisors are 1 and 643.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 643: a twin prime (641 and 643 are both prime); the 117th prime number.
- 2
643 is prime, so its only factors are 1 and 643. It is the 117th prime; the next prime is 647 and the one before is 641.
- 3
The divisors add up to 644; without 643 itself that is 1, so 643 is deficient (1 is less than 643). Euler's totient φ(643) = 642 numbers up to 643 share no factor with it.
- 4
The digits of 643 add up to 13, and repeating that until one digit is left gives the digital root 4. The Collatz sequence (halve if even, else 3n+1) takes 25 steps to reach 1.
643 at a glance
| Property | Value |
|---|---|
| Type | prime |
| Number of divisors | 2 |
| Sum of divisors | 644 |
| Euler totient φ(n) | 642 |
| Square | 413449 |
| Cube | 265847707 |
| Square root | 25.357445 |
| Digit sum / digital root | 13 / 4 |
| Collatz steps to 1 | 25 |
| Scientific notation | 6.43 × |
643 in other forms
| Form | Value |
|---|---|
| In words | six hundred and forty-three |
| Roman numerals | DCXLIII |
| Binary (base 2) | 1010000011 |
| Octal (base 8) | 1203 |
| Hexadecimal (base 16) | 283 |
| Base 3 | 212211 |
| As time | 643 seconds = 10 min 43 s |
Is 643 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 3) | A number is divisible by 4 if the last two digits make a multiple of 4. |
| 5 | No (remainder 3) | 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 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 4) | A number is divisible by 9 if the digits add up to a multiple of 9. |
| 10 | No (remainder 3) | A number is divisible by 10 if the last digit is 0. |
| 11 | No (remainder 5) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 7) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 643 a prime number?
Yes. 643 is divisible only by 1 and itself.
What are the factors of 643?
1, 643.
What is 643 in binary?
1010000011 (hexadecimal 283, octal 1203).
What is the square root of 643?
About 25.3574.
What is 643 in Roman numerals?
DCXLIII.
Is 643 divisible by 3?
No. Its digits add up to 13, which is not a multiple of 3.
What is special about the number 643?
643 is a twin prime (641 and 643 are both prime); the 117th prime number.