The number 1280
1280 is a composite number with 18 divisors. Its prime factorisation is × 5. Divisors (18): 1, 2, 4, 5, 8, 10, 16, 20, 32, 40, 64, 80, 128, 160, 256, 320 … 1280.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
1280 has no famous special property in the usual lists (prime, square, cube, triangular, Fibonacci, palindrome, perfect), but it is still a composite number.
- 2
1280 is composite. Its prime factorisation is
- 3
The divisors add up to 3066; without 1280 itself that is 1786, so 1280 is abundant (1786 is more than 1280). Euler's totient φ(1280) = 512 numbers up to 1280 share no factor with it.
- 4
The digits of 1280 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 13 steps to reach 1.
LaTeX source of the formulas on this page
\[ 1280 = 2^{8} \times 5 \]1280 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 18 |
| Sum of divisors | 3066 |
| Euler totient φ(n) | 512 |
| Square | 1638400 |
| Cube | 2097152000 |
| Square root | 35.777088 (= 16√5) |
| Digit sum / digital root | 11 / 2 |
| Collatz steps to 1 | 13 |
| Scientific notation | 1.28 × |
1280 in other forms
| Form | Value |
|---|---|
| In words | one thousand two hundred and eighty |
| Roman numerals | MCCLXXX |
| Binary (base 2) | 10100000000 |
| Octal (base 8) | 2400 |
| Hexadecimal (base 16) | 500 |
| Base 3 | 1202102 |
| As time | 1280 seconds = 21 min 20 s |
Is 1280 divisible by 2 to 12?
| Divisor | Answer | Rule |
|---|---|---|
| 2 | Yes (1280 ÷ 2 = 640) | 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 (1280 ÷ 4 = 320) | A number is divisible by 4 if the last two digits make a multiple of 4. |
| 5 | Yes (1280 ÷ 5 = 256) | 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 (1280 ÷ 8 = 160) | 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 (1280 ÷ 10 = 128) | 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 8) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 1280 a prime number?
No. 1280 = × 5, so it is divisible by 2.
What are the factors of 1280?
1, 2, 4, 5, 8, 10, 16, 20, 32, 40, 64, 80, 128, 160, 256, 320, 640, 1280.
What is 1280 in binary?
10100000000 (hexadecimal 500, octal 2400).
What is the square root of 1280?
About 35.7771, exactly 16√5.
What is 1280 in Roman numerals?
MCCLXXX.
Is 1280 divisible by 3?
No. Its digits add up to 11, which is not a multiple of 3.
What is special about the number 1280?
It is a composite number with 18 divisors.