The number 81820
81820 is a composite number with 12 divisors. Its prime factorisation is × 5 × 4091. Divisors (12): 1, 2, 4, 5, 10, 20, 4091, 8182, 16364, 20455, 40910, 81820.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 81820: a happy number: repeatedly adding the squares of its digits reaches 1.
- 2
81820 is composite. Its prime factorisation is
- 3
The divisors add up to 171864; without 81820 itself that is 90044, so 81820 is abundant (90044 is more than 81820). Euler's totient φ(81820) = 32720 numbers up to 81820 share no factor with it.
- 4
The digits of 81820 add up to 19, and repeating that until one digit is left gives the digital root 1. The Collatz sequence (halve if even, else 3n+1) takes 37 steps to reach 1.
LaTeX source of the formulas on this page
\[ 81820 = 2^{2} \times 5 \times 4091 \]81820 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 12 |
| Sum of divisors | 171864 |
| Euler totient φ(n) | 32720 |
| Square | 6694512400 |
| Cube | 547745004568000 |
| Square root | 286.041955 (= 2√20455) |
| Digit sum / digital root | 19 / 1 |
| Collatz steps to 1 | 37 |
| Scientific notation | 8.182 × |
81820 in other forms
| Form | Value |
|---|---|
| In words | eighty-one thousand eight hundred and twenty |
| Binary (base 2) | 10011111110011100 |
| Octal (base 8) | 237634 |
| Hexadecimal (base 16) | 13F9C |
| Base 3 | 11011020101 |
| As time | 81820 seconds = 22 h 43 min 40 s |
Is 81820 divisible by 2 to 12?
| Divisor | Answer | Rule |
|---|---|---|
| 2 | Yes (81820 ÷ 2 = 40910) | A number is divisible by 2 if the last digit is even (0, 2, 4, 6, 8). |
| 3 | No (remainder 1) | A number is divisible by 3 if the digits add up to a multiple of 3. |
| 4 | Yes (81820 ÷ 4 = 20455) | A number is divisible by 4 if the last two digits make a multiple of 4. |
| 5 | Yes (81820 ÷ 5 = 16364) | A number is divisible by 5 if the last digit is 0 or 5. |
| 6 | No (remainder 4) | 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 4) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | No (remainder 1) | A number is divisible by 9 if the digits add up to a multiple of 9. |
| 10 | Yes (81820 ÷ 10 = 8182) | A number is divisible by 10 if the last digit is 0. |
| 11 | No (remainder 2) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 4) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 81820 a prime number?
No. 81820 = × 5 × 4091, so it is divisible by 2.
What are the factors of 81820?
1, 2, 4, 5, 10, 20, 4091, 8182, 16364, 20455, 40910, 81820.
What is 81820 in binary?
10011111110011100 (hexadecimal 13F9C, octal 237634).
What is the square root of 81820?
About 286.0420, exactly 2√20455.
Is 81820 divisible by 3?
No. Its digits add up to 19, which is not a multiple of 3.
What is special about the number 81820?
81820 is a happy number: repeatedly adding the squares of its digits reaches 1.