The number 81729
81729 is a composite number with 10 divisors. Its prime factorisation is × 1009. Divisors (10): 1, 3, 9, 27, 81, 1009, 3027, 9081, 27243, 81729.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 81729: a Harshad number: divisible by its digit sum 27.
- 2
81729 is composite. Its prime factorisation is
- 3
The divisors add up to 122210; without 81729 itself that is 40481, so 81729 is deficient (40481 is less than 81729). Euler's totient φ(81729) = 54432 numbers up to 81729 share no factor with it.
- 4
The digits of 81729 add up to 27, and repeating that until one digit is left gives the digital root 9. The Collatz sequence (halve if even, else 3n+1) takes 182 steps to reach 1.
LaTeX source of the formulas on this page
\[ 81729 = 3^{4} \times 1009 \]81729 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 10 |
| Sum of divisors | 122210 |
| Euler totient φ(n) | 54432 |
| Square | 6679629441 |
| Cube | 545919434583489 |
| Square root | 285.882843 (= 9√1009) |
| Digit sum / digital root | 27 / 9 |
| Collatz steps to 1 | 182 |
| Scientific notation | 8.1729 × |
81729 in other forms
| Form | Value |
|---|---|
| In words | eighty-one thousand seven hundred and twenty-nine |
| Binary (base 2) | 10011111101000001 |
| Octal (base 8) | 237501 |
| Hexadecimal (base 16) | 13F41 |
| Base 3 | 11011010000 |
| As time | 81729 seconds = 22 h 42 min 9 s |
Is 81729 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 | Yes (81729 ÷ 3 = 27243) | 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 3) | 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 | Yes (81729 ÷ 9 = 9081) | 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 10) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 9) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 81729 a prime number?
No. 81729 = × 1009, so it is divisible by 3.
What are the factors of 81729?
1, 3, 9, 27, 81, 1009, 3027, 9081, 27243, 81729.
What is 81729 in binary?
10011111101000001 (hexadecimal 13F41, octal 237501).
What is the square root of 81729?
About 285.8828, exactly 9√1009.
Is 81729 divisible by 3?
Yes. Its digits add up to 27, a multiple of 3.
What is special about the number 81729?
81729 is a Harshad number: divisible by its digit sum 27.