The number 809
809 is a twin prime (809 and 811 are both prime) and the 140th prime number. Its only divisors are 1 and 809.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 809: a twin prime (809 and 811 are both prime); the 140th prime number.
- 2
809 is prime, so its only factors are 1 and 809. It is the 140th prime; the next prime is 811 and the one before is 797.
- 3
The divisors add up to 810; without 809 itself that is 1, so 809 is deficient (1 is less than 809). Euler's totient φ(809) = 808 numbers up to 809 share no factor with it.
- 4
The digits of 809 add up to 17, and repeating that until one digit is left gives the digital root 8. The Collatz sequence (halve if even, else 3n+1) takes 46 steps to reach 1.
809 at a glance
| Property | Value |
|---|---|
| Type | prime |
| Number of divisors | 2 |
| Sum of divisors | 810 |
| Euler totient φ(n) | 808 |
| Square | 654481 |
| Cube | 529475129 |
| Square root | 28.442925 |
| Digit sum / digital root | 17 / 8 |
| Collatz steps to 1 | 46 |
| Scientific notation | 8.09 × |
809 in other forms
| Form | Value |
|---|---|
| In words | eight hundred and nine |
| Roman numerals | DCCCIX |
| Binary (base 2) | 1100101001 |
| Octal (base 8) | 1451 |
| Hexadecimal (base 16) | 329 |
| Base 3 | 1002222 |
| As time | 809 seconds = 13 min 29 s |
Is 809 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 2) | 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 | No (remainder 4) | A number is divisible by 5 if the last digit is 0 or 5. |
| 6 | No (remainder 5) | A number is divisible by 6 if it is divisible by both 2 and 3. |
| 7 | No (remainder 4) | 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 1) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | No (remainder 8) | A number is divisible by 9 if the digits add up to a multiple of 9. |
| 10 | No (remainder 9) | A number is divisible by 10 if the last digit is 0. |
| 11 | No (remainder 6) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 5) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 809 a prime number?
Yes. 809 is divisible only by 1 and itself.
What are the factors of 809?
1, 809.
What is 809 in binary?
1100101001 (hexadecimal 329, octal 1451).
What is the square root of 809?
About 28.4429.
What is 809 in Roman numerals?
DCCCIX.
Is 809 divisible by 3?
No. Its digits add up to 17, which is not a multiple of 3.
What is special about the number 809?
809 is a twin prime (809 and 811 are both prime); the 140th prime number.