The number 81981
81981 is a composite number with 6 divisors. Its prime factorisation is × 9109. Divisors (6): 1, 3, 9, 9109, 27327, 81981.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
81981 has no famous special property in the usual lists (prime, square, cube, triangular, Fibonacci, palindrome, perfect), but it is still a composite number.
- 2
81981 is composite. Its prime factorisation is
- 3
The divisors add up to 118430; without 81981 itself that is 36449, so 81981 is deficient (36449 is less than 81981). Euler's totient φ(81981) = 54648 numbers up to 81981 share no factor with it.
- 4
The digits of 81981 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 45 steps to reach 1.
LaTeX source of the formulas on this page
\[ 81981 = 3^{2} \times 9109 \]81981 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 6 |
| Sum of divisors | 118430 |
| Euler totient φ(n) | 54648 |
| Square | 6720884361 |
| Cube | 550984820799141 |
| Square root | 286.323244 (= 3√9109) |
| Digit sum / digital root | 27 / 9 |
| Collatz steps to 1 | 45 |
| Scientific notation | 8.1981 × |
81981 in other forms
| Form | Value |
|---|---|
| In words | eighty-one thousand nine hundred and eighty-one |
| Binary (base 2) | 10100000000111101 |
| Octal (base 8) | 240075 |
| Hexadecimal (base 16) | 1403D |
| Base 3 | 11011110100 |
| As time | 81981 seconds = 22 h 46 min 21 s |
Is 81981 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 (81981 ÷ 3 = 27327) | 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 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 5) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | Yes (81981 ÷ 9 = 9109) | 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 9) | 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 81981 a prime number?
No. 81981 = × 9109, so it is divisible by 3.
What are the factors of 81981?
1, 3, 9, 9109, 27327, 81981.
What is 81981 in binary?
10100000000111101 (hexadecimal 1403D, octal 240075).
What is the square root of 81981?
About 286.3232, exactly 3√9109.
Is 81981 divisible by 3?
Yes. Its digits add up to 27, a multiple of 3.
What is special about the number 81981?
It is a composite number with 6 divisors.