The number 21055
21055 is a composite number with 4 divisors. Its prime factorisation is 5 × 4211. Divisors (4): 1, 5, 4211, 21055.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21055: a semiprime: 5 × 4211, the product of two primes.
- 2
21055 is composite. Its prime factorisation is
- 3
The divisors add up to 25272; without 21055 itself that is 4217, so 21055 is deficient (4217 is less than 21055). Euler's totient φ(21055) = 16840 numbers up to 21055 share no factor with it.
- 4
The digits of 21055 add up to 13, and repeating that until one digit is left gives the digital root 4. The Collatz sequence (halve if even, else 3n+1) takes 87 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21055 = 5 \times 4211 \]
21055 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 4 |
| Sum of divisors | 25272 |
| Euler totient φ(n) | 16840 |
| Square | 443313025 |
| Cube | 9333955741375 |
| Square root | 145.103411 |
| Digit sum / digital root | 13 / 4 |
| Collatz steps to 1 | 87 |
| Scientific notation | 2.1055 × |
21055 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand and fifty-five |
| Binary (base 2) | 101001000111111 |
| Octal (base 8) | 51077 |
| Hexadecimal (base 16) | 523F |
| Base 3 | 1001212211 |
| As time | 21055 seconds = 5 h 50 min 55 s |
Is 21055 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 | No (remainder 1) | 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 (21055 ÷ 5 = 4211) | A number is divisible by 5 if the last digit is 0 or 5. |
| 6 | No (remainder 1) | A number is divisible by 6 if it is divisible by both 2 and 3. |
| 7 | No (remainder 6) | 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 4) | 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 1) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 7) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 21055 a prime number?
No. 21055 = 5 × 4211, so it is divisible by 5.
What are the factors of 21055?
1, 5, 4211, 21055.
What is 21055 in binary?
101001000111111 (hexadecimal 523F, octal 51077).
What is the square root of 21055?
About 145.1034.
Is 21055 divisible by 3?
No. Its digits add up to 13, which is not a multiple of 3.
What is special about the number 21055?
21055 is a semiprime: 5 × 4211, the product of two primes.