The number 685
685 is a composite number with 4 divisors. Its prime factorisation is 5 × 137. Divisors (4): 1, 5, 137, 685.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 685: a semiprime: 5 × 137, the product of two primes.
- 2
685 is composite. Its prime factorisation is
- 3
The divisors add up to 828; without 685 itself that is 143, so 685 is deficient (143 is less than 685). Euler's totient φ(685) = 544 numbers up to 685 share no factor with it.
- 4
The digits of 685 add up to 19, and repeating that until one digit is left gives the digital root 1. The Collatz sequence (halve if even, else 3n+1) takes 126 steps to reach 1.
LaTeX source of the formulas on this page
\[ 685 = 5 \times 137 \]
685 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 4 |
| Sum of divisors | 828 |
| Euler totient φ(n) | 544 |
| Square | 469225 |
| Cube | 321419125 |
| Square root | 26.172505 |
| Digit sum / digital root | 19 / 1 |
| Collatz steps to 1 | 126 |
| Scientific notation | 6.85 × |
685 in other forms
| Form | Value |
|---|---|
| In words | six hundred and eighty-five |
| Roman numerals | DCLXXXV |
| Binary (base 2) | 1010101101 |
| Octal (base 8) | 1255 |
| Hexadecimal (base 16) | 2AD |
| Base 3 | 221101 |
| As time | 685 seconds = 11 min 25 s |
Is 685 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 1) | A number is divisible by 4 if the last two digits make a multiple of 4. |
| 5 | Yes (685 ÷ 5 = 137) | 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 5) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | No (remainder 1) | A number is divisible by 9 if the digits add up to a multiple of 9. |
| 10 | No (remainder 5) | A number is divisible by 10 if the last digit is 0. |
| 11 | No (remainder 3) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 1) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 685 a prime number?
No. 685 = 5 × 137, so it is divisible by 5.
What are the factors of 685?
1, 5, 137, 685.
What is 685 in binary?
1010101101 (hexadecimal 2AD, octal 1255).
What is the square root of 685?
About 26.1725.
What is 685 in Roman numerals?
DCLXXXV.
Is 685 divisible by 3?
No. Its digits add up to 19, which is not a multiple of 3.
What is special about the number 685?
685 is a semiprime: 5 × 137, the product of two primes.