The number 21508
21508 is a composite number with 12 divisors. Its prime factorisation is × 19 × 283. Divisors (12): 1, 2, 4, 19, 38, 76, 283, 566, 1132, 5377, 10754, 21508.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21508: a happy number: repeatedly adding the squares of its digits reaches 1.
- 2
21508 is composite. Its prime factorisation is
- 3
The divisors add up to 39760; without 21508 itself that is 18252, so 21508 is deficient (18252 is less than 21508). Euler's totient φ(21508) = 10152 numbers up to 21508 share no factor with it.
- 4
The digits of 21508 add up to 16, and repeating that until one digit is left gives the digital root 7. The Collatz sequence (halve if even, else 3n+1) takes 74 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21508 = 2^{2} \times 19 \times 283 \]21508 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 12 |
| Sum of divisors | 39760 |
| Euler totient φ(n) | 10152 |
| Square | 462594064 |
| Cube | 9949473128512 |
| Square root | 146.656060 (= 2√5377) |
| Digit sum / digital root | 16 / 7 |
| Collatz steps to 1 | 74 |
| Scientific notation | 2.1508 × |
21508 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand five hundred and eight |
| Binary (base 2) | 101010000000100 |
| Octal (base 8) | 52004 |
| Hexadecimal (base 16) | 5404 |
| Base 3 | 1002111121 |
| As time | 21508 seconds = 5 h 58 min 28 s |
Is 21508 divisible by 2 to 12?
| Divisor | Answer | Rule |
|---|---|---|
| 2 | Yes (21508 ÷ 2 = 10754) | 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 | Yes (21508 ÷ 4 = 5377) | A number is divisible by 4 if the last two digits make a multiple of 4. |
| 5 | No (remainder 3) | A number is divisible by 5 if the last digit is 0 or 5. |
| 6 | No (remainder 4) | A number is divisible by 6 if it is divisible by both 2 and 3. |
| 7 | No (remainder 4) | 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 4) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | No (remainder 7) | A number is divisible by 9 if the digits add up to a multiple of 9. |
| 10 | No (remainder 8) | 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 4) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 21508 a prime number?
No. 21508 = × 19 × 283, so it is divisible by 2.
What are the factors of 21508?
1, 2, 4, 19, 38, 76, 283, 566, 1132, 5377, 10754, 21508.
What is 21508 in binary?
101010000000100 (hexadecimal 5404, octal 52004).
What is the square root of 21508?
About 146.6561, exactly 2√5377.
Is 21508 divisible by 3?
No. Its digits add up to 16, which is not a multiple of 3.
What is special about the number 21508?
21508 is a happy number: repeatedly adding the squares of its digits reaches 1.