The number 81389
81389 is a composite number with 12 divisors. Its prime factorisation is × 11 × 151. Divisors (12): 1, 7, 11, 49, 77, 151, 539, 1057, 1661, 7399, 11627, 81389.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 81389: a happy number: repeatedly adding the squares of its digits reaches 1.
- 2
81389 is composite. Its prime factorisation is
- 3
The divisors add up to 103968; without 81389 itself that is 22579, so 81389 is deficient (22579 is less than 81389). Euler's totient φ(81389) = 63000 numbers up to 81389 share no factor with it.
- 4
The digits of 81389 add up to 29, and repeating that until one digit is left gives the digital root 2. The Collatz sequence (halve if even, else 3n+1) takes 76 steps to reach 1.
LaTeX source of the formulas on this page
\[ 81389 = 7^{2} \times 11 \times 151 \]81389 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 12 |
| Sum of divisors | 103968 |
| Euler totient φ(n) | 63000 |
| Square | 6624169321 |
| Cube | 539134516866869 |
| Square root | 285.287574 (= 7√1661) |
| Digit sum / digital root | 29 / 2 |
| Collatz steps to 1 | 76 |
| Scientific notation | 8.1389 × |
81389 in other forms
| Form | Value |
|---|---|
| In words | eighty-one thousand three hundred and eighty-nine |
| Binary (base 2) | 10011110111101101 |
| Octal (base 8) | 236755 |
| Hexadecimal (base 16) | 13DED |
| Base 3 | 11010122102 |
| As time | 81389 seconds = 22 h 36 min 29 s |
Is 81389 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 (81389 ÷ 7 = 11627) | 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 2) | 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 | Yes (81389 ÷ 11 = 7399) | 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 81389 a prime number?
No. 81389 = × 11 × 151, so it is divisible by 7.
What are the factors of 81389?
1, 7, 11, 49, 77, 151, 539, 1057, 1661, 7399, 11627, 81389.
What is 81389 in binary?
10011110111101101 (hexadecimal 13DED, octal 236755).
What is the square root of 81389?
About 285.2876, exactly 7√1661.
Is 81389 divisible by 3?
No. Its digits add up to 29, which is not a multiple of 3.
What is special about the number 81389?
81389 is a happy number: repeatedly adding the squares of its digits reaches 1.