The number 21128
21128 is a composite number with 16 divisors. Its prime factorisation is × 19 × 139. Divisors (16): 1, 2, 4, 8, 19, 38, 76, 139, 152, 278, 556, 1112, 2641, 5282, 10564, 21128.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
21128 has no famous special property in the usual lists (prime, square, cube, triangular, Fibonacci, palindrome, perfect), but it is still a composite number.
- 2
21128 is composite. Its prime factorisation is
- 3
The divisors add up to 42000; without 21128 itself that is 20872, so 21128 is deficient (20872 is less than 21128). Euler's totient φ(21128) = 9936 numbers up to 21128 share no factor with it.
- 4
The digits of 21128 add up to 14, and repeating that until one digit is left gives the digital root 5. The Collatz sequence (halve if even, else 3n+1) takes 105 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21128 = 2^{3} \times 19 \times 139 \]21128 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 16 |
| Sum of divisors | 42000 |
| Euler totient φ(n) | 9936 |
| Square | 446392384 |
| Cube | 9431378289152 |
| Square root | 145.354738 (= 2√5282) |
| Digit sum / digital root | 14 / 5 |
| Collatz steps to 1 | 105 |
| Scientific notation | 2.1128 × |
21128 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand one hundred and twenty-eight |
| Binary (base 2) | 101001010001000 |
| Octal (base 8) | 51210 |
| Hexadecimal (base 16) | 5288 |
| Base 3 | 1001222112 |
| As time | 21128 seconds = 5 h 52 min 8 s |
Is 21128 divisible by 2 to 12?
| Divisor | Answer | Rule |
|---|---|---|
| 2 | Yes (21128 ÷ 2 = 10564) | 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 (21128 ÷ 4 = 5282) | 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 2) | 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 (21128 ÷ 8 = 2641) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | No (remainder 5) | 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 21128 a prime number?
No. 21128 = × 19 × 139, so it is divisible by 2.
What are the factors of 21128?
1, 2, 4, 8, 19, 38, 76, 139, 152, 278, 556, 1112, 2641, 5282, 10564, 21128.
What is 21128 in binary?
101001010001000 (hexadecimal 5288, octal 51210).
What is the square root of 21128?
About 145.3547, exactly 2√5282.
Is 21128 divisible by 3?
No. Its digits add up to 14, which is not a multiple of 3.
What is special about the number 21128?
It is a composite number with 16 divisors.