The number 28821
28821 is a composite number with 8 divisors. Its prime factorisation is 3 × 13 × 739. Divisors (8): 1, 3, 13, 39, 739, 2217, 9607, 28821.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
28821 has no famous special property in the usual lists (prime, square, cube, triangular, Fibonacci, palindrome, perfect), but it is still a composite number.
- 2
28821 is composite. Its prime factorisation is
- 3
The divisors add up to 41440; without 28821 itself that is 12619, so 28821 is deficient (12619 is less than 28821). Euler's totient φ(28821) = 17712 numbers up to 28821 share no factor with it.
- 4
The digits of 28821 add up to 21, and repeating that until one digit is left gives the digital root 3. The Collatz sequence (halve if even, else 3n+1) takes 165 steps to reach 1.
LaTeX source of the formulas on this page
\[ 28821 = 3 \times 13 \times 739 \]
28821 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 8 |
| Sum of divisors | 41440 |
| Euler totient φ(n) | 17712 |
| Square | 830650041 |
| Cube | 23940164831661 |
| Square root | 169.767488 |
| Digit sum / digital root | 21 / 3 |
| Collatz steps to 1 | 165 |
| Scientific notation | 2.8821 × |
28821 in other forms
| Form | Value |
|---|---|
| In words | twenty-eight thousand eight hundred and twenty-one |
| Binary (base 2) | 111000010010101 |
| Octal (base 8) | 70225 |
| Hexadecimal (base 16) | 7095 |
| Base 3 | 1110112110 |
| As time | 28821 seconds = 8 h 0 min 21 s |
Is 28821 divisible by 2 to 12?
| Divisor | Answer | Rule |
|---|---|---|
| 2 | No (remainder 1) | A number is divisible by 2 if the last digit is even (0, 2, 4, 6, 8). |
| 3 | Yes (28821 ÷ 3 = 9607) | A number is divisible by 3 if the digits add up to a multiple of 3. |
| 4 | No (remainder 1) | A number is divisible by 4 if the last two digits make a multiple of 4. |
| 5 | No (remainder 1) | A number is divisible by 5 if the last digit is 0 or 5. |
| 6 | No (remainder 3) | A number is divisible by 6 if it is divisible by both 2 and 3. |
| 7 | No (remainder 2) | 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 | No (remainder 5) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | No (remainder 3) | A number is divisible by 9 if the digits add up to a multiple of 9. |
| 10 | No (remainder 1) | A number is divisible by 10 if the last digit is 0. |
| 11 | No (remainder 1) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 9) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 28821 a prime number?
No. 28821 = 3 × 13 × 739, so it is divisible by 3.
What are the factors of 28821?
1, 3, 13, 39, 739, 2217, 9607, 28821.
What is 28821 in binary?
111000010010101 (hexadecimal 7095, octal 70225).
What is the square root of 28821?
About 169.7675.
Is 28821 divisible by 3?
Yes. Its digits add up to 21, a multiple of 3.
What is special about the number 28821?
It is a composite number with 8 divisors.