The number 21789
21789 is a composite number with 10 divisors. Its prime factorisation is × 269. Divisors (10): 1, 3, 9, 27, 81, 269, 807, 2421, 7263, 21789.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21789: a Harshad number: divisible by its digit sum 27.
- 2
21789 is composite. Its prime factorisation is
- 3
The divisors add up to 32670; without 21789 itself that is 10881, so 21789 is deficient (10881 is less than 21789). Euler's totient φ(21789) = 14472 numbers up to 21789 share no factor with it.
- 4
The digits of 21789 add up to 27, and repeating that until one digit is left gives the digital root 9. The Collatz sequence (halve if even, else 3n+1) takes 100 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21789 = 3^{4} \times 269 \]21789 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 10 |
| Sum of divisors | 32670 |
| Euler totient φ(n) | 14472 |
| Square | 474760521 |
| Cube | 10344556992069 |
| Square root | 147.610975 (= 9√269) |
| Digit sum / digital root | 27 / 9 |
| Collatz steps to 1 | 100 |
| Scientific notation | 2.1789 × |
21789 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand seven hundred and eighty-nine |
| Binary (base 2) | 101010100011101 |
| Octal (base 8) | 52435 |
| Hexadecimal (base 16) | 551D |
| Base 3 | 1002220000 |
| As time | 21789 seconds = 6 h 3 min 9 s |
Is 21789 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 (21789 ÷ 3 = 7263) | A number is divisible by 3 if the digits add up to a multiple of 3. |
| 4 | No (remainder 1) | A number is divisible by 4 if the last two digits make a multiple of 4. |
| 5 | No (remainder 4) | 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 5) | 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 5) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | Yes (21789 ÷ 9 = 2421) | A number is divisible by 9 if the digits add up to a multiple of 9. |
| 10 | No (remainder 9) | 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 9) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 21789 a prime number?
No. 21789 = × 269, so it is divisible by 3.
What are the factors of 21789?
1, 3, 9, 27, 81, 269, 807, 2421, 7263, 21789.
What is 21789 in binary?
101010100011101 (hexadecimal 551D, octal 52435).
What is the square root of 21789?
About 147.6110, exactly 9√269.
Is 21789 divisible by 3?
Yes. Its digits add up to 27, a multiple of 3.
What is special about the number 21789?
21789 is a Harshad number: divisible by its digit sum 27.