The number 21788
21788 is a composite number with 12 divisors. Its prime factorisation is × 13 × 419. Divisors (12): 1, 2, 4, 13, 26, 52, 419, 838, 1676, 5447, 10894, 21788.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21788: a Harshad number: divisible by its digit sum 26.
- 2
21788 is composite. Its prime factorisation is
- 3
The divisors add up to 41160; without 21788 itself that is 19372, so 21788 is deficient (19372 is less than 21788). Euler's totient φ(21788) = 10032 numbers up to 21788 share no factor with it.
- 4
The digits of 21788 add up to 26, and repeating that until one digit is left gives the digital root 8. The Collatz sequence (halve if even, else 3n+1) takes 100 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21788 = 2^{2} \times 13 \times 419 \]21788 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 12 |
| Sum of divisors | 41160 |
| Euler totient φ(n) | 10032 |
| Square | 474716944 |
| Cube | 10343132775872 |
| Square root | 147.607588 (= 2√5447) |
| Digit sum / digital root | 26 / 8 |
| Collatz steps to 1 | 100 |
| Scientific notation | 2.1788 × |
21788 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand seven hundred and eighty-eight |
| Binary (base 2) | 101010100011100 |
| Octal (base 8) | 52434 |
| Hexadecimal (base 16) | 551C |
| Base 3 | 1002212222 |
| As time | 21788 seconds = 6 h 3 min 8 s |
Is 21788 divisible by 2 to 12?
| Divisor | Answer | Rule |
|---|---|---|
| 2 | Yes (21788 ÷ 2 = 10894) | 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 | Yes (21788 ÷ 4 = 5447) | 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 2) | 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 8) | 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 8) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 8) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 21788 a prime number?
No. 21788 = × 13 × 419, so it is divisible by 2.
What are the factors of 21788?
1, 2, 4, 13, 26, 52, 419, 838, 1676, 5447, 10894, 21788.
What is 21788 in binary?
101010100011100 (hexadecimal 551C, octal 52434).
What is the square root of 21788?
About 147.6076, exactly 2√5447.
Is 21788 divisible by 3?
No. Its digits add up to 26, which is not a multiple of 3.
What is special about the number 21788?
21788 is a Harshad number: divisible by its digit sum 26.