The number 21855
21855 is a composite number with 16 divisors. Its prime factorisation is 3 × 5 × 31 × 47. Divisors (16): 1, 3, 5, 15, 31, 47, 93, 141, 155, 235, 465, 705, 1457, 4371, 7285, 21855.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
21855 has no famous special property in the usual lists (prime, square, cube, triangular, Fibonacci, palindrome, perfect), but it is still a composite number.
- 2
21855 is composite. Its prime factorisation is
- 3
The divisors add up to 36864; without 21855 itself that is 15009, so 21855 is deficient (15009 is less than 21855). Euler's totient φ(21855) = 11040 numbers up to 21855 share no factor with it.
- 4
The digits of 21855 add up to 21, and repeating that until one digit is left gives the digital root 3. The Collatz sequence (halve if even, else 3n+1) takes 56 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21855 = 3 \times 5 \times 31 \times 47 \]
21855 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 16 |
| Sum of divisors | 36864 |
| Euler totient φ(n) | 11040 |
| Square | 477641025 |
| Cube | 10438844601375 |
| Square root | 147.834367 |
| Digit sum / digital root | 21 / 3 |
| Collatz steps to 1 | 56 |
| Scientific notation | 2.1855 × |
21855 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand eight hundred and fifty-five |
| Binary (base 2) | 101010101011111 |
| Octal (base 8) | 52537 |
| Hexadecimal (base 16) | 555F |
| Base 3 | 1002222110 |
| As time | 21855 seconds = 6 h 4 min 15 s |
Is 21855 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 (21855 ÷ 3 = 7285) | 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 (21855 ÷ 5 = 4371) | 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 1) | 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 3) | 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 9) | 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 21855 a prime number?
No. 21855 = 3 × 5 × 31 × 47, so it is divisible by 3.
What are the factors of 21855?
1, 3, 5, 15, 31, 47, 93, 141, 155, 235, 465, 705, 1457, 4371, 7285, 21855.
What is 21855 in binary?
101010101011111 (hexadecimal 555F, octal 52537).
What is the square root of 21855?
About 147.8344.
Is 21855 divisible by 3?
Yes. Its digits add up to 21, a multiple of 3.
What is special about the number 21855?
It is a composite number with 16 divisors.