The number 81810
81810 is a triangular number: 1 + 2 + … + 404 = 81810. Its prime factorisation is 2 × × 5 × 101. Divisors (40): 1, 2, 3, 5, 6, 9, 10, 15, 18, 27, 30, 45, 54, 81, 90, 101 … 81810.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 81810: a triangular number: 1 + 2 + … + 404 = 81810; a happy number: repeatedly adding the squares of its digits reaches 1; a Harshad number: divisible by its digit sum 18.
- 2
81810 is composite. Its prime factorisation is
- 3
The divisors add up to 222156; without 81810 itself that is 140346, so 81810 is abundant (140346 is more than 81810). Euler's totient φ(81810) = 21600 numbers up to 81810 share no factor with it.
- 4
The digits of 81810 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 182 steps to reach 1.
LaTeX source of the formulas on this page
\[ 81810 = 2 \times 3^{4} \times 5 \times 101 \]81810 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 40 |
| Sum of divisors | 222156 |
| Euler totient φ(n) | 21600 |
| Square | 6692876100 |
| Cube | 547544193741000 |
| Square root | 286.024474 (= 9√1010) |
| Digit sum / digital root | 18 / 9 |
| Collatz steps to 1 | 182 |
| Scientific notation | 8.181 × |
81810 in other forms
| Form | Value |
|---|---|
| In words | eighty-one thousand eight hundred and ten |
| Binary (base 2) | 10011111110010010 |
| Octal (base 8) | 237622 |
| Hexadecimal (base 16) | 13F92 |
| Base 3 | 11011020000 |
| As time | 81810 seconds = 22 h 43 min 30 s |
Is 81810 divisible by 2 to 12?
| Divisor | Answer | Rule |
|---|---|---|
| 2 | Yes (81810 ÷ 2 = 40905) | A number is divisible by 2 if the last digit is even (0, 2, 4, 6, 8). |
| 3 | Yes (81810 ÷ 3 = 27270) | A number is divisible by 3 if the digits add up to a multiple of 3. |
| 4 | No (remainder 2) | A number is divisible by 4 if the last two digits make a multiple of 4. |
| 5 | Yes (81810 ÷ 5 = 16362) | A number is divisible by 5 if the last digit is 0 or 5. |
| 6 | Yes (81810 ÷ 6 = 13635) | A number is divisible by 6 if it is divisible by both 2 and 3. |
| 7 | No (remainder 1) | 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 2) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | Yes (81810 ÷ 9 = 9090) | A number is divisible by 9 if the digits add up to a multiple of 9. |
| 10 | Yes (81810 ÷ 10 = 8181) | 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 6) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 81810 a prime number?
No. 81810 = 2 × × 5 × 101, so it is divisible by 2.
What are the factors of 81810?
1, 2, 3, 5, 6, 9, 10, 15, 18, 27, 30, 45, 54, 81, 90, 101, 135, 162, 202, 270, 303, 405, 505, 606, 810, 909, 1010, 1515, 1818, 2727, 3030, 4545, 5454, 8181, 9090, 13635, 16362, 27270, 40905, 81810.
What is 81810 in binary?
10011111110010010 (hexadecimal 13F92, octal 237622).
What is the square root of 81810?
About 286.0245, exactly 9√1010.
Is 81810 divisible by 3?
Yes. Its digits add up to 18, a multiple of 3.
What is special about the number 81810?
81810 is a triangular number: 1 + 2 + … + 404 = 81810; a happy number: repeatedly adding the squares of its digits reaches 1; a Harshad number: divisible by its digit sum 18.