The number 28720
28720 is a composite number with 20 divisors. Its prime factorisation is × 5 × 359. Divisors (20): 1, 2, 4, 5, 8, 10, 16, 20, 40, 80, 359, 718, 1436, 1795, 2872, 3590 … 28720.
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How to work it out
- 1
28720 has no famous special property in the usual lists (prime, square, cube, triangular, Fibonacci, palindrome, perfect), but it is still a composite number.
- 2
28720 is composite. Its prime factorisation is
- 3
The divisors add up to 66960; without 28720 itself that is 38240, so 28720 is abundant (38240 is more than 28720). Euler's totient φ(28720) = 11456 numbers up to 28720 share no factor with it.
- 4
The digits of 28720 add up to 19, and repeating that until one digit is left gives the digital root 1. The Collatz sequence (halve if even, else 3n+1) takes 72 steps to reach 1.
LaTeX source of the formulas on this page
\[ 28720 = 2^{4} \times 5 \times 359 \]28720 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 20 |
| Sum of divisors | 66960 |
| Euler totient φ(n) | 11456 |
| Square | 824838400 |
| Cube | 23689358848000 |
| Square root | 169.469761 (= 4√1795) |
| Digit sum / digital root | 19 / 1 |
| Collatz steps to 1 | 72 |
| Scientific notation | 2.872 × |
28720 in other forms
| Form | Value |
|---|---|
| In words | twenty-eight thousand seven hundred and twenty |
| Binary (base 2) | 111000000110000 |
| Octal (base 8) | 70060 |
| Hexadecimal (base 16) | 7030 |
| Base 3 | 1110101201 |
| As time | 28720 seconds = 7 h 58 min 40 s |
Is 28720 divisible by 2 to 12?
| Divisor | Answer | Rule |
|---|---|---|
| 2 | Yes (28720 ÷ 2 = 14360) | 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 (28720 ÷ 4 = 7180) | A number is divisible by 4 if the last two digits make a multiple of 4. |
| 5 | Yes (28720 ÷ 5 = 5744) | 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 | 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 (28720 ÷ 8 = 3590) | 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 (28720 ÷ 10 = 2872) | A number is divisible by 10 if the last digit is 0. |
| 11 | No (remainder 10) | 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 28720 a prime number?
No. 28720 = × 5 × 359, so it is divisible by 2.
What are the factors of 28720?
1, 2, 4, 5, 8, 10, 16, 20, 40, 80, 359, 718, 1436, 1795, 2872, 3590, 5744, 7180, 14360, 28720.
What is 28720 in binary?
111000000110000 (hexadecimal 7030, octal 70060).
What is the square root of 28720?
About 169.4698, exactly 4√1795.
Is 28720 divisible by 3?
No. Its digits add up to 19, which is not a multiple of 3.
What is special about the number 28720?
It is a composite number with 20 divisors.