The number 21280
21280 is a composite number with 48 divisors. Its prime factorisation is × 5 × 7 × 19. Divisors (48): 1, 2, 4, 5, 7, 8, 10, 14, 16, 19, 20, 28, 32, 35, 38, 40 … 21280.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
21280 has no famous special property in the usual lists (prime, square, cube, triangular, Fibonacci, palindrome, perfect), but it is still a composite number.
- 2
21280 is composite. Its prime factorisation is
- 3
The divisors add up to 60480; without 21280 itself that is 39200, so 21280 is abundant (39200 is more than 21280). Euler's totient φ(21280) = 6912 numbers up to 21280 share no factor with it.
- 4
The digits of 21280 add up to 13, 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
\[ 21280 = 2^{5} \times 5 \times 7 \times 19 \]21280 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 48 |
| Sum of divisors | 60480 |
| Euler totient φ(n) | 6912 |
| Square | 452838400 |
| Cube | 9636401152000 |
| Square root | 145.876660 (= 4√1330) |
| Digit sum / digital root | 13 / 4 |
| Collatz steps to 1 | 56 |
| Scientific notation | 2.128 × |
21280 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand two hundred and eighty |
| Binary (base 2) | 101001100100000 |
| Octal (base 8) | 51440 |
| Hexadecimal (base 16) | 5320 |
| Base 3 | 1002012011 |
| As time | 21280 seconds = 5 h 54 min 40 s |
Is 21280 divisible by 2 to 12?
| Divisor | Answer | Rule |
|---|---|---|
| 2 | Yes (21280 ÷ 2 = 10640) | 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 (21280 ÷ 4 = 5320) | A number is divisible by 4 if the last two digits make a multiple of 4. |
| 5 | Yes (21280 ÷ 5 = 4256) | 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 (21280 ÷ 7 = 3040) | 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 (21280 ÷ 8 = 2660) | 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 | Yes (21280 ÷ 10 = 2128) | A number is divisible by 10 if the last digit is 0. |
| 11 | No (remainder 6) | 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 21280 a prime number?
No. 21280 = × 5 × 7 × 19, so it is divisible by 2.
What are the factors of 21280?
1, 2, 4, 5, 7, 8, 10, 14, 16, 19, 20, 28, 32, 35, 38, 40, 56, 70, 76, 80, 95, 112, 133, 140, 152, 160, 190, 224, 266, 280, 304, 380, 532, 560, 608, 665, 760, 1064, 1120, 1330, 1520, 2128, 2660, 3040, 4256, 5320, 10640, 21280.
What is 21280 in binary?
101001100100000 (hexadecimal 5320, octal 51440).
What is the square root of 21280?
About 145.8767, exactly 4√1330.
Is 21280 divisible by 3?
No. Its digits add up to 13, which is not a multiple of 3.
What is special about the number 21280?
It is a composite number with 48 divisors.