The number 21784
21784 is a composite number with 16 divisors. Its prime factorisation is × 7 × 389. Divisors (16): 1, 2, 4, 7, 8, 14, 28, 56, 389, 778, 1556, 2723, 3112, 5446, 10892, 21784.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
21784 has no famous special property in the usual lists (prime, square, cube, triangular, Fibonacci, palindrome, perfect), but it is still a composite number.
- 2
21784 is composite. Its prime factorisation is
- 3
The divisors add up to 46800; without 21784 itself that is 25016, so 21784 is abundant (25016 is more than 21784). Euler's totient φ(21784) = 9312 numbers up to 21784 share no factor with it.
- 4
The digits of 21784 add up to 22, and repeating that until one digit is left gives the digital root 4. The Collatz sequence (halve if even, else 3n+1) takes 56 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21784 = 2^{3} \times 7 \times 389 \]21784 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 16 |
| Sum of divisors | 46800 |
| Euler totient φ(n) | 9312 |
| Square | 474542656 |
| Cube | 10337437218304 |
| Square root | 147.594038 (= 2√5446) |
| Digit sum / digital root | 22 / 4 |
| Collatz steps to 1 | 56 |
| Scientific notation | 2.1784 × |
21784 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand seven hundred and eighty-four |
| Binary (base 2) | 101010100011000 |
| Octal (base 8) | 52430 |
| Hexadecimal (base 16) | 5518 |
| Base 3 | 1002212211 |
| As time | 21784 seconds = 6 h 3 min 4 s |
Is 21784 divisible by 2 to 12?
| Divisor | Answer | Rule |
|---|---|---|
| 2 | Yes (21784 ÷ 2 = 10892) | 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 (21784 ÷ 4 = 5446) | 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 4) | A number is divisible by 6 if it is divisible by both 2 and 3. |
| 7 | Yes (21784 ÷ 7 = 3112) | 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 | Yes (21784 ÷ 8 = 2723) | 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 4) | A number is divisible by 10 if the last digit is 0. |
| 11 | No (remainder 4) | 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 21784 a prime number?
No. 21784 = × 7 × 389, so it is divisible by 2.
What are the factors of 21784?
1, 2, 4, 7, 8, 14, 28, 56, 389, 778, 1556, 2723, 3112, 5446, 10892, 21784.
What is 21784 in binary?
101010100011000 (hexadecimal 5518, octal 52430).
What is the square root of 21784?
About 147.5940, exactly 2√5446.
Is 21784 divisible by 3?
No. Its digits add up to 22, which is not a multiple of 3.
What is special about the number 21784?
It is a composite number with 16 divisors.