The number 21075
21075 is a composite number with 12 divisors. Its prime factorisation is 3 × × 281. Divisors (12): 1, 3, 5, 15, 25, 75, 281, 843, 1405, 4215, 7025, 21075.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21075: a happy number: repeatedly adding the squares of its digits reaches 1; a Harshad number: divisible by its digit sum 15.
- 2
21075 is composite. Its prime factorisation is
- 3
The divisors add up to 34968; without 21075 itself that is 13893, so 21075 is deficient (13893 is less than 21075). Euler's totient φ(21075) = 11200 numbers up to 21075 share no factor with it.
- 4
The digits of 21075 add up to 15, and repeating that until one digit is left gives the digital root 6. The Collatz sequence (halve if even, else 3n+1) takes 79 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21075 = 3 \times 5^{2} \times 281 \]21075 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 12 |
| Sum of divisors | 34968 |
| Euler totient φ(n) | 11200 |
| Square | 444155625 |
| Cube | 9360579796875 |
| Square root | 145.172311 (= 5√843) |
| Digit sum / digital root | 15 / 6 |
| Collatz steps to 1 | 79 |
| Scientific notation | 2.1075 × |
21075 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand and seventy-five |
| Binary (base 2) | 101001001010011 |
| Octal (base 8) | 51123 |
| Hexadecimal (base 16) | 5253 |
| Base 3 | 1001220120 |
| As time | 21075 seconds = 5 h 51 min 15 s |
Is 21075 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 (21075 ÷ 3 = 7025) | A number is divisible by 3 if the digits add up to a multiple of 3. |
| 4 | No (remainder 3) | A number is divisible by 4 if the last two digits make a multiple of 4. |
| 5 | Yes (21075 ÷ 5 = 4215) | 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 5) | 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 3) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | No (remainder 6) | A number is divisible by 9 if the digits add up to a multiple of 9. |
| 10 | No (remainder 5) | A number is divisible by 10 if the last digit is 0. |
| 11 | No (remainder 10) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 3) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 21075 a prime number?
No. 21075 = 3 × × 281, so it is divisible by 3.
What are the factors of 21075?
1, 3, 5, 15, 25, 75, 281, 843, 1405, 4215, 7025, 21075.
What is 21075 in binary?
101001001010011 (hexadecimal 5253, octal 51123).
What is the square root of 21075?
About 145.1723, exactly 5√843.
Is 21075 divisible by 3?
Yes. Its digits add up to 15, a multiple of 3.
What is special about the number 21075?
21075 is a happy number: repeatedly adding the squares of its digits reaches 1; a Harshad number: divisible by its digit sum 15.