The number 21155
21155 is a composite number with 4 divisors. Its prime factorisation is 5 × 4231. Divisors (4): 1, 5, 4231, 21155.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21155: a semiprime: 5 × 4231, the product of two primes.
- 2
21155 is composite. Its prime factorisation is
- 3
The divisors add up to 25392; without 21155 itself that is 4237, so 21155 is deficient (4237 is less than 21155). Euler's totient φ(21155) = 16920 numbers up to 21155 share no factor with it.
- 4
The digits of 21155 add up to 14, and repeating that until one digit is left gives the digital root 5. The Collatz sequence (halve if even, else 3n+1) takes 56 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21155 = 5 \times 4231 \]
21155 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 4 |
| Sum of divisors | 25392 |
| Euler totient φ(n) | 16920 |
| Square | 447534025 |
| Cube | 9467582298875 |
| Square root | 145.447585 |
| Digit sum / digital root | 14 / 5 |
| Collatz steps to 1 | 56 |
| Scientific notation | 2.1155 × |
21155 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand one hundred and fifty-five |
| Binary (base 2) | 101001010100011 |
| Octal (base 8) | 51243 |
| Hexadecimal (base 16) | 52A3 |
| Base 3 | 1002000112 |
| As time | 21155 seconds = 5 h 52 min 35 s |
Is 21155 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 2) | 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 (21155 ÷ 5 = 4231) | A number is divisible by 5 if the last digit is 0 or 5. |
| 6 | No (remainder 5) | 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 3) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | No (remainder 5) | 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 2) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 11) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 21155 a prime number?
No. 21155 = 5 × 4231, so it is divisible by 5.
What are the factors of 21155?
1, 5, 4231, 21155.
What is 21155 in binary?
101001010100011 (hexadecimal 52A3, octal 51243).
What is the square root of 21155?
About 145.4476.
Is 21155 divisible by 3?
No. Its digits add up to 14, which is not a multiple of 3.
What is special about the number 21155?
21155 is a semiprime: 5 × 4231, the product of two primes.