The number 81381
81381 is a composite number with 4 divisors. Its prime factorisation is 3 × 27127. Divisors (4): 1, 3, 27127, 81381.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 81381: a happy number: repeatedly adding the squares of its digits reaches 1; a semiprime: 3 × 27127, the product of two primes.
- 2
81381 is composite. Its prime factorisation is
- 3
The divisors add up to 108512; without 81381 itself that is 27131, so 81381 is deficient (27131 is less than 81381). Euler's totient φ(81381) = 54252 numbers up to 81381 share no factor with it.
- 4
The digits of 81381 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 89 steps to reach 1.
LaTeX source of the formulas on this page
\[ 81381 = 3 \times 27127 \]
81381 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 4 |
| Sum of divisors | 108512 |
| Euler totient φ(n) | 54252 |
| Square | 6622867161 |
| Cube | 538975552429341 |
| Square root | 285.273553 |
| Digit sum / digital root | 21 / 3 |
| Collatz steps to 1 | 89 |
| Scientific notation | 8.1381 × |
81381 in other forms
| Form | Value |
|---|---|
| In words | eighty-one thousand three hundred and eighty-one |
| Binary (base 2) | 10011110111100101 |
| Octal (base 8) | 236745 |
| Hexadecimal (base 16) | 13DE5 |
| Base 3 | 11010122010 |
| As time | 81381 seconds = 22 h 36 min 21 s |
Is 81381 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 (81381 ÷ 3 = 27127) | 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 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 | No (remainder 6) | 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 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 3) | 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 81381 a prime number?
No. 81381 = 3 × 27127, so it is divisible by 3.
What are the factors of 81381?
1, 3, 27127, 81381.
What is 81381 in binary?
10011110111100101 (hexadecimal 13DE5, octal 236745).
What is the square root of 81381?
About 285.2736.
Is 81381 divisible by 3?
Yes. Its digits add up to 21, a multiple of 3.
What is special about the number 81381?
81381 is a happy number: repeatedly adding the squares of its digits reaches 1; a semiprime: 3 × 27127, the product of two primes.