The number 81813
81813 is a composite number with 4 divisors. Its prime factorisation is 3 × 27271. Divisors (4): 1, 3, 27271, 81813.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 81813: a happy number: repeatedly adding the squares of its digits reaches 1; a semiprime: 3 × 27271, the product of two primes.
- 2
81813 is composite. Its prime factorisation is
- 3
The divisors add up to 109088; without 81813 itself that is 27275, so 81813 is deficient (27275 is less than 81813). Euler's totient φ(81813) = 54540 numbers up to 81813 share no factor with it.
- 4
The digits of 81813 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 138 steps to reach 1.
LaTeX source of the formulas on this page
\[ 81813 = 3 \times 27271 \]
81813 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 4 |
| Sum of divisors | 109088 |
| Euler totient φ(n) | 54540 |
| Square | 6693366969 |
| Cube | 547604431834797 |
| Square root | 286.029719 |
| Digit sum / digital root | 21 / 3 |
| Collatz steps to 1 | 138 |
| Scientific notation | 8.1813 × |
81813 in other forms
| Form | Value |
|---|---|
| In words | eighty-one thousand eight hundred and thirteen |
| Binary (base 2) | 10011111110010101 |
| Octal (base 8) | 237625 |
| Hexadecimal (base 16) | 13F95 |
| Base 3 | 11011020010 |
| As time | 81813 seconds = 22 h 43 min 33 s |
Is 81813 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 (81813 ÷ 3 = 27271) | 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 3) | 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 | No (remainder 3) | A number is divisible by 9 if the digits add up to a multiple of 9. |
| 10 | No (remainder 3) | A number is divisible by 10 if the last digit is 0. |
| 11 | No (remainder 6) | 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 81813 a prime number?
No. 81813 = 3 × 27271, so it is divisible by 3.
What are the factors of 81813?
1, 3, 27271, 81813.
What is 81813 in binary?
10011111110010101 (hexadecimal 13F95, octal 237625).
What is the square root of 81813?
About 286.0297.
Is 81813 divisible by 3?
Yes. Its digits add up to 21, a multiple of 3.
What is special about the number 81813?
81813 is a happy number: repeatedly adding the squares of its digits reaches 1; a semiprime: 3 × 27271, the product of two primes.