The number 280
280 is a composite number with 16 divisors. Its prime factorisation is × 5 × 7. Divisors (16): 1, 2, 4, 5, 7, 8, 10, 14, 20, 28, 35, 40, 56, 70, 140, 280.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 280: a happy number: repeatedly adding the squares of its digits reaches 1; a Harshad number: divisible by its digit sum 10.
- 2
280 is composite. Its prime factorisation is
- 3
The divisors add up to 720; without 280 itself that is 440, so 280 is abundant (440 is more than 280). Euler's totient φ(280) = 96 numbers up to 280 share no factor with it.
- 4
The digits of 280 add up to 10, and repeating that until one digit is left gives the digital root 1. The Collatz sequence (halve if even, else 3n+1) takes 16 steps to reach 1.
LaTeX source of the formulas on this page
\[ 280 = 2^{3} \times 5 \times 7 \]280 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 16 |
| Sum of divisors | 720 |
| Euler totient φ(n) | 96 |
| Square | 78400 |
| Cube | 21952000 |
| Square root | 16.733201 (= 2√70) |
| Digit sum / digital root | 10 / 1 |
| Collatz steps to 1 | 16 |
| Scientific notation | 2.8 × |
280 in other forms
| Form | Value |
|---|---|
| In words | two hundred and eighty |
| Roman numerals | CCLXXX |
| Binary (base 2) | 100011000 |
| Octal (base 8) | 430 |
| Hexadecimal (base 16) | 118 |
| Base 3 | 101101 |
| As time | 280 seconds = 4 min 40 s |
Is 280 divisible by 2 to 12?
| Divisor | Answer | Rule |
|---|---|---|
| 2 | Yes (280 ÷ 2 = 140) | 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 (280 ÷ 4 = 70) | A number is divisible by 4 if the last two digits make a multiple of 4. |
| 5 | Yes (280 ÷ 5 = 56) | 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 (280 ÷ 7 = 40) | 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 (280 ÷ 8 = 35) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | No (remainder 1) | A number is divisible by 9 if the digits add up to a multiple of 9. |
| 10 | Yes (280 ÷ 10 = 28) | A number is divisible by 10 if the last digit is 0. |
| 11 | No (remainder 5) | 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 280 a prime number?
No. 280 = × 5 × 7, so it is divisible by 2.
What are the factors of 280?
1, 2, 4, 5, 7, 8, 10, 14, 20, 28, 35, 40, 56, 70, 140, 280.
What is 280 in binary?
100011000 (hexadecimal 118, octal 430).
What is the square root of 280?
About 16.7332, exactly 2√70.
What is 280 in Roman numerals?
CCLXXX.
Is 280 divisible by 3?
No. Its digits add up to 10, which is not a multiple of 3.
What is special about the number 280?
280 is a happy number: repeatedly adding the squares of its digits reaches 1; a Harshad number: divisible by its digit sum 10.