The number 646
646 is a palindrome: it reads 646 backwards too. Its prime factorisation is 2 × 17 × 19. Divisors (8): 1, 2, 17, 19, 34, 38, 323, 646.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 646: a palindrome: it reads 646 backwards too.
- 2
646 is composite. Its prime factorisation is
- 3
The divisors add up to 1080; without 646 itself that is 434, so 646 is deficient (434 is less than 646). Euler's totient φ(646) = 288 numbers up to 646 share no factor with it.
- 4
The digits of 646 add up to 16, and repeating that until one digit is left gives the digital root 7. The Collatz sequence (halve if even, else 3n+1) takes 100 steps to reach 1.
LaTeX source of the formulas on this page
\[ 646 = 2 \times 17 \times 19 \]
646 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 8 |
| Sum of divisors | 1080 |
| Euler totient φ(n) | 288 |
| Square | 417316 |
| Cube | 269586136 |
| Square root | 25.416530 |
| Digit sum / digital root | 16 / 7 |
| Collatz steps to 1 | 100 |
| Scientific notation | 6.46 × |
646 in other forms
| Form | Value |
|---|---|
| In words | six hundred and forty-six |
| Roman numerals | DCXLVI |
| Binary (base 2) | 1010000110 |
| Octal (base 8) | 1206 |
| Hexadecimal (base 16) | 286 |
| Base 3 | 212221 |
| As time | 646 seconds = 10 min 46 s |
Is 646 divisible by 2 to 12?
| Divisor | Answer | Rule |
|---|---|---|
| 2 | Yes (646 ÷ 2 = 323) | 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 2) | 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 4) | A number is divisible by 6 if it is divisible by both 2 and 3. |
| 7 | No (remainder 2) | 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 6) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | No (remainder 7) | A number is divisible by 9 if the digits add up to a multiple of 9. |
| 10 | No (remainder 6) | 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 10) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 646 a prime number?
No. 646 = 2 × 17 × 19, so it is divisible by 2.
What are the factors of 646?
1, 2, 17, 19, 34, 38, 323, 646.
What is 646 in binary?
1010000110 (hexadecimal 286, octal 1206).
What is the square root of 646?
About 25.4165.
What is 646 in Roman numerals?
DCXLVI.
Is 646 divisible by 3?
No. Its digits add up to 16, which is not a multiple of 3.
What is special about the number 646?
646 is a palindrome: it reads 646 backwards too.