The number 21555
21555 is a composite number with 12 divisors. Its prime factorisation is × 5 × 479. Divisors (12): 1, 3, 5, 9, 15, 45, 479, 1437, 2395, 4311, 7185, 21555.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
21555 has no famous special property in the usual lists (prime, square, cube, triangular, Fibonacci, palindrome, perfect), but it is still a composite number.
- 2
21555 is composite. Its prime factorisation is
- 3
The divisors add up to 37440; without 21555 itself that is 15885, so 21555 is deficient (15885 is less than 21555). Euler's totient φ(21555) = 11472 numbers up to 21555 share no factor with it.
- 4
The digits of 21555 add up to 18, and repeating that until one digit is left gives the digital root 9. The Collatz sequence (halve if even, else 3n+1) takes 149 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21555 = 3^{2} \times 5 \times 479 \]21555 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 12 |
| Sum of divisors | 37440 |
| Euler totient φ(n) | 11472 |
| Square | 464618025 |
| Cube | 10014841528875 |
| Square root | 146.816212 (= 3√2395) |
| Digit sum / digital root | 18 / 9 |
| Collatz steps to 1 | 149 |
| Scientific notation | 2.1555 × |
21555 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand five hundred and fifty-five |
| Binary (base 2) | 101010000110011 |
| Octal (base 8) | 52063 |
| Hexadecimal (base 16) | 5433 |
| Base 3 | 1002120100 |
| As time | 21555 seconds = 5 h 59 min 15 s |
Is 21555 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 (21555 ÷ 3 = 7185) | 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 (21555 ÷ 5 = 4311) | 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 2) | 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 | Yes (21555 ÷ 9 = 2395) | 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 6) | 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 21555 a prime number?
No. 21555 = × 5 × 479, so it is divisible by 3.
What are the factors of 21555?
1, 3, 5, 9, 15, 45, 479, 1437, 2395, 4311, 7185, 21555.
What is 21555 in binary?
101010000110011 (hexadecimal 5433, octal 52063).
What is the square root of 21555?
About 146.8162, exactly 3√2395.
Is 21555 divisible by 3?
Yes. Its digits add up to 18, a multiple of 3.
What is special about the number 21555?
It is a composite number with 12 divisors.