The number 27821
27821 is a composite number with 4 divisors. Its prime factorisation is 43 × 647. Divisors (4): 1, 43, 647, 27821.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 27821: a semiprime: 43 × 647, the product of two primes.
- 2
27821 is composite. Its prime factorisation is
- 3
The divisors add up to 28512; without 27821 itself that is 691, so 27821 is deficient (691 is less than 27821). Euler's totient φ(27821) = 27132 numbers up to 27821 share no factor with it.
- 4
The digits of 27821 add up to 20, and repeating that until one digit is left gives the digital root 2. The Collatz sequence (halve if even, else 3n+1) takes 152 steps to reach 1.
LaTeX source of the formulas on this page
\[ 27821 = 43 \times 647 \]
27821 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 4 |
| Sum of divisors | 28512 |
| Euler totient φ(n) | 27132 |
| Square | 774008041 |
| Cube | 21533677708661 |
| Square root | 166.796283 |
| Digit sum / digital root | 20 / 2 |
| Collatz steps to 1 | 152 |
| Scientific notation | 2.7821 × |
27821 in other forms
| Form | Value |
|---|---|
| In words | twenty-seven thousand eight hundred and twenty-one |
| Binary (base 2) | 110110010101101 |
| Octal (base 8) | 66255 |
| Hexadecimal (base 16) | 6CAD |
| Base 3 | 1102011102 |
| As time | 27821 seconds = 7 h 43 min 41 s |
Is 27821 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 2) | 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 5) | A number is divisible by 6 if it is divisible by both 2 and 3. |
| 7 | No (remainder 3) | 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 2) | 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 2) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 5) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 27821 a prime number?
No. 27821 = 43 × 647, so it is divisible by 43.
What are the factors of 27821?
1, 43, 647, 27821.
What is 27821 in binary?
110110010101101 (hexadecimal 6CAD, octal 66255).
What is the square root of 27821?
About 166.7963.
Is 27821 divisible by 3?
No. Its digits add up to 20, which is not a multiple of 3.
What is special about the number 27821?
27821 is a semiprime: 43 × 647, the product of two primes.