The number 21440
21440 is a composite number with 28 divisors. Its prime factorisation is × 5 × 67. Divisors (28): 1, 2, 4, 5, 8, 10, 16, 20, 32, 40, 64, 67, 80, 134, 160, 268 … 21440.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
21440 has no famous special property in the usual lists (prime, square, cube, triangular, Fibonacci, palindrome, perfect), but it is still a composite number.
- 2
21440 is composite. Its prime factorisation is
- 3
The divisors add up to 51816; without 21440 itself that is 30376, so 21440 is abundant (30376 is more than 21440). Euler's totient φ(21440) = 8448 numbers up to 21440 share no factor with it.
- 4
The digits of 21440 add up to 11, and repeating that until one digit is left gives the digital root 2. The Collatz sequence (halve if even, else 3n+1) takes 74 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21440 = 2^{6} \times 5 \times 67 \]21440 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 28 |
| Sum of divisors | 51816 |
| Euler totient φ(n) | 8448 |
| Square | 459673600 |
| Cube | 9855401984000 |
| Square root | 146.424042 (= 8√335) |
| Digit sum / digital root | 11 / 2 |
| Collatz steps to 1 | 74 |
| Scientific notation | 2.144 × |
21440 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand four hundred and forty |
| Binary (base 2) | 101001111000000 |
| Octal (base 8) | 51700 |
| Hexadecimal (base 16) | 53C0 |
| Base 3 | 1002102002 |
| As time | 21440 seconds = 5 h 57 min 20 s |
Is 21440 divisible by 2 to 12?
| Divisor | Answer | Rule |
|---|---|---|
| 2 | Yes (21440 ÷ 2 = 10720) | 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 (21440 ÷ 4 = 5360) | A number is divisible by 4 if the last two digits make a multiple of 4. |
| 5 | Yes (21440 ÷ 5 = 4288) | 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 6) | 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 (21440 ÷ 8 = 2680) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | No (remainder 2) | A number is divisible by 9 if the digits add up to a multiple of 9. |
| 10 | Yes (21440 ÷ 10 = 2144) | A number is divisible by 10 if the last digit is 0. |
| 11 | No (remainder 1) | 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 21440 a prime number?
No. 21440 = × 5 × 67, so it is divisible by 2.
What are the factors of 21440?
1, 2, 4, 5, 8, 10, 16, 20, 32, 40, 64, 67, 80, 134, 160, 268, 320, 335, 536, 670, 1072, 1340, 2144, 2680, 4288, 5360, 10720, 21440.
What is 21440 in binary?
101001111000000 (hexadecimal 53C0, octal 51700).
What is the square root of 21440?
About 146.4240, exactly 8√335.
Is 21440 divisible by 3?
No. Its digits add up to 11, which is not a multiple of 3.
What is special about the number 21440?
It is a composite number with 28 divisors.