The number 81291
81291 is a composite number with 16 divisors. Its prime factorisation is 3 × × 79. Divisors (16): 1, 3, 7, 21, 49, 79, 147, 237, 343, 553, 1029, 1659, 3871, 11613, 27097, 81291.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 81291: a Harshad number: divisible by its digit sum 21.
- 2
81291 is composite. Its prime factorisation is
- 3
The divisors add up to 128000; without 81291 itself that is 46709, so 81291 is deficient (46709 is less than 81291). Euler's totient φ(81291) = 45864 numbers up to 81291 share no factor with it.
- 4
The digits of 81291 add up to 21, and repeating that until one digit is left gives the digital root 3. The Collatz sequence (halve if even, else 3n+1) takes 182 steps to reach 1.
LaTeX source of the formulas on this page
\[ 81291 = 3 \times 7^{3} \times 79 \]81291 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 16 |
| Sum of divisors | 128000 |
| Euler totient φ(n) | 45864 |
| Square | 6608226681 |
| Cube | 537189355125171 |
| Square root | 285.115766 (= 7√1659) |
| Digit sum / digital root | 21 / 3 |
| Collatz steps to 1 | 182 |
| Scientific notation | 8.1291 × |
81291 in other forms
| Form | Value |
|---|---|
| In words | eighty-one thousand two hundred and ninety-one |
| Binary (base 2) | 10011110110001011 |
| Octal (base 8) | 236613 |
| Hexadecimal (base 16) | 13D8B |
| Base 3 | 11010111210 |
| As time | 81291 seconds = 22 h 34 min 51 s |
Is 81291 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 (81291 ÷ 3 = 27097) | A number is divisible by 3 if the digits add up to a multiple of 3. |
| 4 | No (remainder 3) | A number is divisible by 4 if the last two digits make a multiple of 4. |
| 5 | No (remainder 1) | 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 | Yes (81291 ÷ 7 = 11613) | 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 3) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | No (remainder 3) | A number is divisible by 9 if the digits add up to a multiple of 9. |
| 10 | No (remainder 1) | A number is divisible by 10 if the last digit is 0. |
| 11 | No (remainder 1) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 3) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 81291 a prime number?
No. 81291 = 3 × × 79, so it is divisible by 3.
What are the factors of 81291?
1, 3, 7, 21, 49, 79, 147, 237, 343, 553, 1029, 1659, 3871, 11613, 27097, 81291.
What is 81291 in binary?
10011110110001011 (hexadecimal 13D8B, octal 236613).
What is the square root of 81291?
About 285.1158, exactly 7√1659.
Is 81291 divisible by 3?
Yes. Its digits add up to 21, a multiple of 3.
What is special about the number 81291?
81291 is a Harshad number: divisible by its digit sum 21.