The number 28021
28021 is a composite number with 4 divisors. Its prime factorisation is 7 × 4003. Divisors (4): 1, 7, 4003, 28021.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 28021: a semiprime: 7 × 4003, the product of two primes.
- 2
28021 is composite. Its prime factorisation is
- 3
The divisors add up to 32032; without 28021 itself that is 4011, so 28021 is deficient (4011 is less than 28021). Euler's totient φ(28021) = 24012 numbers up to 28021 share no factor with it.
- 4
The digits of 28021 add up to 13, and repeating that until one digit is left gives the digital root 4. The Collatz sequence (halve if even, else 3n+1) takes 33 steps to reach 1.
LaTeX source of the formulas on this page
\[ 28021 = 7 \times 4003 \]
28021 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 4 |
| Sum of divisors | 32032 |
| Euler totient φ(n) | 24012 |
| Square | 785176441 |
| Cube | 22001429053261 |
| Square root | 167.394743 |
| Digit sum / digital root | 13 / 4 |
| Collatz steps to 1 | 33 |
| Scientific notation | 2.8021 × |
28021 in other forms
| Form | Value |
|---|---|
| In words | twenty-eight thousand and twenty-one |
| Binary (base 2) | 110110101110101 |
| Octal (base 8) | 66565 |
| Hexadecimal (base 16) | 6D75 |
| Base 3 | 1102102211 |
| As time | 28021 seconds = 7 h 47 min 1 s |
Is 28021 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 | No (remainder 1) | 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 1) | A number is divisible by 6 if it is divisible by both 2 and 3. |
| 7 | Yes (28021 ÷ 7 = 4003) | 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 4) | 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 4) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 1) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 28021 a prime number?
No. 28021 = 7 × 4003, so it is divisible by 7.
What are the factors of 28021?
1, 7, 4003, 28021.
What is 28021 in binary?
110110101110101 (hexadecimal 6D75, octal 66565).
What is the square root of 28021?
About 167.3947.
Is 28021 divisible by 3?
No. Its digits add up to 13, which is not a multiple of 3.
What is special about the number 28021?
28021 is a semiprime: 7 × 4003, the product of two primes.