The number 21255
21255 is a composite number with 16 divisors. Its prime factorisation is 3 × 5 × 13 × 109. Divisors (16): 1, 3, 5, 13, 15, 39, 65, 109, 195, 327, 545, 1417, 1635, 4251, 7085, 21255.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21255: a Harshad number: divisible by its digit sum 15.
- 2
21255 is composite. Its prime factorisation is
- 3
The divisors add up to 36960; without 21255 itself that is 15705, so 21255 is deficient (15705 is less than 21255). Euler's totient φ(21255) = 10368 numbers up to 21255 share no factor with it.
- 4
The digits of 21255 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 149 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21255 = 3 \times 5 \times 13 \times 109 \]
21255 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 16 |
| Sum of divisors | 36960 |
| Euler totient φ(n) | 10368 |
| Square | 451775025 |
| Cube | 9602478156375 |
| Square root | 145.790946 |
| Digit sum / digital root | 15 / 6 |
| Collatz steps to 1 | 149 |
| Scientific notation | 2.1255 × |
21255 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand two hundred and fifty-five |
| Binary (base 2) | 101001100000111 |
| Octal (base 8) | 51407 |
| Hexadecimal (base 16) | 5307 |
| Base 3 | 1002011020 |
| As time | 21255 seconds = 5 h 54 min 15 s |
Is 21255 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 (21255 ÷ 3 = 7085) | 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 (21255 ÷ 5 = 4251) | 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 7) | 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 3) | 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 21255 a prime number?
No. 21255 = 3 × 5 × 13 × 109, so it is divisible by 3.
What are the factors of 21255?
1, 3, 5, 13, 15, 39, 65, 109, 195, 327, 545, 1417, 1635, 4251, 7085, 21255.
What is 21255 in binary?
101001100000111 (hexadecimal 5307, octal 51407).
What is the square root of 21255?
About 145.7909.
Is 21255 divisible by 3?
Yes. Its digits add up to 15, a multiple of 3.
What is special about the number 21255?
21255 is a Harshad number: divisible by its digit sum 15.