The number 21428
21428 is a composite number with 12 divisors. Its prime factorisation is × 11 × 487. Divisors (12): 1, 2, 4, 11, 22, 44, 487, 974, 1948, 5357, 10714, 21428.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
21428 has no famous special property in the usual lists (prime, square, cube, triangular, Fibonacci, palindrome, perfect), but it is still a composite number.
- 2
21428 is composite. Its prime factorisation is
- 3
The divisors add up to 40992; without 21428 itself that is 19564, so 21428 is deficient (19564 is less than 21428). Euler's totient φ(21428) = 9720 numbers up to 21428 share no factor with it.
- 4
The digits of 21428 add up to 17, and repeating that until one digit is left gives the digital root 8. The Collatz sequence (halve if even, else 3n+1) takes 30 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21428 = 2^{2} \times 11 \times 487 \]21428 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 12 |
| Sum of divisors | 40992 |
| Euler totient φ(n) | 9720 |
| Square | 459159184 |
| Cube | 9838862994752 |
| Square root | 146.383059 (= 2√5357) |
| Digit sum / digital root | 17 / 8 |
| Collatz steps to 1 | 30 |
| Scientific notation | 2.1428 × |
21428 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand four hundred and twenty-eight |
| Binary (base 2) | 101001110110100 |
| Octal (base 8) | 51664 |
| Hexadecimal (base 16) | 53B4 |
| Base 3 | 1002101122 |
| As time | 21428 seconds = 5 h 57 min 8 s |
Is 21428 divisible by 2 to 12?
| Divisor | Answer | Rule |
|---|---|---|
| 2 | Yes (21428 ÷ 2 = 10714) | 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 (21428 ÷ 4 = 5357) | 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 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 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 | Yes (21428 ÷ 11 = 1948) | 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 21428 a prime number?
No. 21428 = × 11 × 487, so it is divisible by 2.
What are the factors of 21428?
1, 2, 4, 11, 22, 44, 487, 974, 1948, 5357, 10714, 21428.
What is 21428 in binary?
101001110110100 (hexadecimal 53B4, octal 51664).
What is the square root of 21428?
About 146.3831, exactly 2√5357.
Is 21428 divisible by 3?
No. Its digits add up to 17, which is not a multiple of 3.
What is special about the number 21428?
It is a composite number with 12 divisors.