The number 805
805 is a composite number with 8 divisors. Its prime factorisation is 5 × 7 × 23. Divisors (8): 1, 5, 7, 23, 35, 115, 161, 805.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
805 has no famous special property in the usual lists (prime, square, cube, triangular, Fibonacci, palindrome, perfect), but it is still a composite number.
- 2
805 is composite. Its prime factorisation is
- 3
The divisors add up to 1152; without 805 itself that is 347, so 805 is deficient (347 is less than 805). Euler's totient φ(805) = 528 numbers up to 805 share no factor with it.
- 4
The digits of 805 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 20 steps to reach 1.
LaTeX source of the formulas on this page
\[ 805 = 5 \times 7 \times 23 \]
805 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 8 |
| Sum of divisors | 1152 |
| Euler totient φ(n) | 528 |
| Square | 648025 |
| Cube | 521660125 |
| Square root | 28.372522 |
| Digit sum / digital root | 13 / 4 |
| Collatz steps to 1 | 20 |
| Scientific notation | 8.05 × |
805 in other forms
| Form | Value |
|---|---|
| In words | eight hundred and five |
| Roman numerals | DCCCV |
| Binary (base 2) | 1100100101 |
| Octal (base 8) | 1445 |
| Hexadecimal (base 16) | 325 |
| Base 3 | 1002211 |
| As time | 805 seconds = 13 min 25 s |
Is 805 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 (805 ÷ 5 = 161) | 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 | Yes (805 ÷ 7 = 115) | 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 2) | 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 805 a prime number?
No. 805 = 5 × 7 × 23, so it is divisible by 5.
What are the factors of 805?
1, 5, 7, 23, 35, 115, 161, 805.
What is 805 in binary?
1100100101 (hexadecimal 325, octal 1445).
What is the square root of 805?
About 28.3725.
What is 805 in Roman numerals?
DCCCV.
Is 805 divisible by 3?
No. Its digits add up to 13, which is not a multiple of 3.
What is special about the number 805?
It is a composite number with 8 divisors.