The number 81809
81809 is a composite number with 16 divisors. Its prime factorisation is 7 × 13 × 29 × 31. Divisors (16): 1, 7, 13, 29, 31, 91, 203, 217, 377, 403, 899, 2639, 2821, 6293, 11687, 81809.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
81809 has no famous special property in the usual lists (prime, square, cube, triangular, Fibonacci, palindrome, perfect), but it is still a composite number.
- 2
81809 is composite. Its prime factorisation is
- 3
The divisors add up to 107520; without 81809 itself that is 25711, so 81809 is deficient (25711 is less than 81809). Euler's totient φ(81809) = 60480 numbers up to 81809 share no factor with it.
- 4
The digits of 81809 add up to 26, and repeating that until one digit is left gives the digital root 8. The Collatz sequence (halve if even, else 3n+1) takes 182 steps to reach 1.
LaTeX source of the formulas on this page
\[ 81809 = 7 \times 13 \times 29 \times 31 \]
81809 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 16 |
| Sum of divisors | 107520 |
| Euler totient φ(n) | 60480 |
| Square | 6692712481 |
| Cube | 547524115358129 |
| Square root | 286.022726 |
| Digit sum / digital root | 26 / 8 |
| Collatz steps to 1 | 182 |
| Scientific notation | 8.1809 × |
81809 in other forms
| Form | Value |
|---|---|
| In words | eighty-one thousand eight hundred and nine |
| Binary (base 2) | 10011111110010001 |
| Octal (base 8) | 237621 |
| Hexadecimal (base 16) | 13F91 |
| Base 3 | 11011012222 |
| As time | 81809 seconds = 22 h 43 min 29 s |
Is 81809 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 | Yes (81809 ÷ 7 = 11687) | 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 2) | 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 81809 a prime number?
No. 81809 = 7 × 13 × 29 × 31, so it is divisible by 7.
What are the factors of 81809?
1, 7, 13, 29, 31, 91, 203, 217, 377, 403, 899, 2639, 2821, 6293, 11687, 81809.
What is 81809 in binary?
10011111110010001 (hexadecimal 13F91, octal 237621).
What is the square root of 81809?
About 286.0227.
Is 81809 divisible by 3?
No. Its digits add up to 26, which is not a multiple of 3.
What is special about the number 81809?
It is a composite number with 16 divisors.