The number 21081
21081 is a composite number with 4 divisors. Its prime factorisation is 3 × 7027. Divisors (4): 1, 3, 7027, 21081.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21081: a happy number: repeatedly adding the squares of its digits reaches 1; a semiprime: 3 × 7027, the product of two primes.
- 2
21081 is composite. Its prime factorisation is
- 3
The divisors add up to 28112; without 21081 itself that is 7031, so 21081 is deficient (7031 is less than 21081). Euler's totient φ(21081) = 14052 numbers up to 21081 share no factor with it.
- 4
The digits of 21081 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 193 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21081 = 3 \times 7027 \]
21081 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 4 |
| Sum of divisors | 28112 |
| Euler totient φ(n) | 14052 |
| Square | 444408561 |
| Cube | 9368576874441 |
| Square root | 145.192975 |
| Digit sum / digital root | 12 / 3 |
| Collatz steps to 1 | 193 |
| Scientific notation | 2.1081 × |
21081 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand and eighty-one |
| Binary (base 2) | 101001001011001 |
| Octal (base 8) | 51131 |
| Hexadecimal (base 16) | 5259 |
| Base 3 | 1001220210 |
| As time | 21081 seconds = 5 h 51 min 21 s |
Is 21081 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 (21081 ÷ 3 = 7027) | 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 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 1) | 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 5) | 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 21081 a prime number?
No. 21081 = 3 × 7027, so it is divisible by 3.
What are the factors of 21081?
1, 3, 7027, 21081.
What is 21081 in binary?
101001001011001 (hexadecimal 5259, octal 51131).
What is the square root of 21081?
About 145.1930.
Is 21081 divisible by 3?
Yes. Its digits add up to 12, a multiple of 3.
What is special about the number 21081?
21081 is a happy number: repeatedly adding the squares of its digits reaches 1; a semiprime: 3 × 7027, the product of two primes.