The number 81021
81021 is a composite number with 8 divisors. Its prime factorisation is 3 × 113 × 239. Divisors (8): 1, 3, 113, 239, 339, 717, 27007, 81021.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 81021: a happy number: repeatedly adding the squares of its digits reaches 1.
- 2
81021 is composite. Its prime factorisation is
- 3
The divisors add up to 109440; without 81021 itself that is 28419, so 81021 is deficient (28419 is less than 81021). Euler's totient φ(81021) = 53312 numbers up to 81021 share no factor with it.
- 4
The digits of 81021 add up to 12, and repeating that until one digit is left gives the digital root 3. The Collatz sequence (halve if even, else 3n+1) takes 174 steps to reach 1.
LaTeX source of the formulas on this page
\[ 81021 = 3 \times 113 \times 239 \]
81021 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 8 |
| Sum of divisors | 109440 |
| Euler totient φ(n) | 53312 |
| Square | 6564402441 |
| Cube | 531854450172261 |
| Square root | 284.641880 |
| Digit sum / digital root | 12 / 3 |
| Collatz steps to 1 | 174 |
| Scientific notation | 8.1021 × |
81021 in other forms
| Form | Value |
|---|---|
| In words | eighty-one thousand and twenty-one |
| Binary (base 2) | 10011110001111101 |
| Octal (base 8) | 236175 |
| Hexadecimal (base 16) | 13C7D |
| Base 3 | 11010010210 |
| As time | 81021 seconds = 22 h 30 min 21 s |
Is 81021 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 (81021 ÷ 3 = 27007) | 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 3) | 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 1) | 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 81021 a prime number?
No. 81021 = 3 × 113 × 239, so it is divisible by 3.
What are the factors of 81021?
1, 3, 113, 239, 339, 717, 27007, 81021.
What is 81021 in binary?
10011110001111101 (hexadecimal 13C7D, octal 236175).
What is the square root of 81021?
About 284.6419.
Is 81021 divisible by 3?
Yes. Its digits add up to 12, a multiple of 3.
What is special about the number 81021?
81021 is a happy number: repeatedly adding the squares of its digits reaches 1.