The number 8181
8181 is a composite number with 10 divisors. Its prime factorisation is × 101. Divisors (10): 1, 3, 9, 27, 81, 101, 303, 909, 2727, 8181.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 8181: a happy number: repeatedly adding the squares of its digits reaches 1.
- 2
8181 is composite. Its prime factorisation is
- 3
The divisors add up to 12342; without 8181 itself that is 4161, so 8181 is deficient (4161 is less than 8181). Euler's totient φ(8181) = 5400 numbers up to 8181 share no factor with it.
- 4
The digits of 8181 add up to 18, and repeating that until one digit is left gives the digital root 9. The Collatz sequence (halve if even, else 3n+1) takes 65 steps to reach 1.
LaTeX source of the formulas on this page
\[ 8181 = 3^{4} \times 101 \]8181 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 10 |
| Sum of divisors | 12342 |
| Euler totient φ(n) | 5400 |
| Square | 66928761 |
| Cube | 547544193741 |
| Square root | 90.448881 (= 9√101) |
| Digit sum / digital root | 18 / 9 |
| Collatz steps to 1 | 65 |
| Scientific notation | 8.181 × |
8181 in other forms
| Form | Value |
|---|---|
| In words | eight thousand one hundred and eighty-one |
| Binary (base 2) | 1111111110101 |
| Octal (base 8) | 17765 |
| Hexadecimal (base 16) | 1FF5 |
| Base 3 | 102020000 |
| As time | 8181 seconds = 2 h 16 min 21 s |
Is 8181 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 (8181 ÷ 3 = 2727) | 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 5) | 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 (8181 ÷ 9 = 909) | 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 8) | 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 8181 a prime number?
No. 8181 = × 101, so it is divisible by 3.
What are the factors of 8181?
1, 3, 9, 27, 81, 101, 303, 909, 2727, 8181.
What is 8181 in binary?
1111111110101 (hexadecimal 1FF5, octal 17765).
What is the square root of 8181?
About 90.4489, exactly 9√101.
Is 8181 divisible by 3?
Yes. Its digits add up to 18, a multiple of 3.
What is special about the number 8181?
8181 is a happy number: repeatedly adding the squares of its digits reaches 1.