The number 728
728 is a composite number with 16 divisors. Its prime factorisation is × 7 × 13. Divisors (16): 1, 2, 4, 7, 8, 13, 14, 26, 28, 52, 56, 91, 104, 182, 364, 728.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
728 has no famous special property in the usual lists (prime, square, cube, triangular, Fibonacci, palindrome, perfect), but it is still a composite number.
- 2
728 is composite. Its prime factorisation is
- 3
The divisors add up to 1680; without 728 itself that is 952, so 728 is abundant (952 is more than 728). Euler's totient φ(728) = 288 numbers up to 728 share no factor with it.
- 4
The digits of 728 add up to 17, and repeating that until one digit is left gives the digital root 8. The Collatz sequence (halve if even, else 3n+1) takes 95 steps to reach 1.
LaTeX source of the formulas on this page
\[ 728 = 2^{3} \times 7 \times 13 \]728 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 16 |
| Sum of divisors | 1680 |
| Euler totient φ(n) | 288 |
| Square | 529984 |
| Cube | 385828352 |
| Square root | 26.981475 (= 2√182) |
| Digit sum / digital root | 17 / 8 |
| Collatz steps to 1 | 95 |
| Scientific notation | 7.28 × |
728 in other forms
| Form | Value |
|---|---|
| In words | seven hundred and twenty-eight |
| Roman numerals | DCCXXVIII |
| Binary (base 2) | 1011011000 |
| Octal (base 8) | 1330 |
| Hexadecimal (base 16) | 2D8 |
| Base 3 | 222222 |
| As time | 728 seconds = 12 min 8 s |
Is 728 divisible by 2 to 12?
| Divisor | Answer | Rule |
|---|---|---|
| 2 | Yes (728 ÷ 2 = 364) | 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 (728 ÷ 4 = 182) | 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 | Yes (728 ÷ 7 = 104) | 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 (728 ÷ 8 = 91) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | No (remainder 8) | 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 2) | 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 728 a prime number?
No. 728 = × 7 × 13, so it is divisible by 2.
What are the factors of 728?
1, 2, 4, 7, 8, 13, 14, 26, 28, 52, 56, 91, 104, 182, 364, 728.
What is 728 in binary?
1011011000 (hexadecimal 2D8, octal 1330).
What is the square root of 728?
About 26.9815, exactly 2√182.
What is 728 in Roman numerals?
DCCXXVIII.
Is 728 divisible by 3?
No. Its digits add up to 17, which is not a multiple of 3.
What is special about the number 728?
It is a composite number with 16 divisors.