The number 85
85 is a binary palindrome (1010101). Its prime factorisation is 5 × 17. Divisors (4): 1, 5, 17, 85.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 85: a binary palindrome (1010101); a semiprime: 5 × 17, the product of two primes.
- 2
85 is composite. Its prime factorisation is
- 3
The divisors add up to 108; without 85 itself that is 23, so 85 is deficient (23 is less than 85). Euler's totient φ(85) = 64 numbers up to 85 share no factor with it.
- 4
The digits of 85 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 9 steps to reach 1.
LaTeX source of the formulas on this page
\[ 85 = 5 \times 17 \]
85 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 4 |
| Sum of divisors | 108 |
| Euler totient φ(n) | 64 |
| Square | 7225 |
| Cube | 614125 |
| Square root | 9.219544 |
| Digit sum / digital root | 13 / 4 |
| Collatz steps to 1 | 9 |
| Scientific notation | 8.5 × |
85 in other forms
| Form | Value |
|---|---|
| In words | eighty-five |
| Roman numerals | LXXXV |
| Binary (base 2) | 1010101 |
| Octal (base 8) | 125 |
| Hexadecimal (base 16) | 55 |
| Base 3 | 10011 |
| As time | 85 seconds = 1 min 25 s |
Is 85 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 (85 ÷ 5 = 17) | 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 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 5) | 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 5) | 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 1) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 85 a prime number?
No. 85 = 5 × 17, so it is divisible by 5.
What are the factors of 85?
1, 5, 17, 85.
What is 85 in binary?
1010101 (hexadecimal 55, octal 125).
What is the square root of 85?
About 9.2195.
What is 85 in Roman numerals?
LXXXV.
Is 85 divisible by 3?
No. Its digits add up to 13, which is not a multiple of 3.
What is special about the number 85?
85 is a binary palindrome (1010101); a semiprime: 5 × 17, the product of two primes.