The number 18821
18821 is a composite number with 8 divisors. Its prime factorisation is 11 × 29 × 59. Divisors (8): 1, 11, 29, 59, 319, 649, 1711, 18821.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
18821 has no famous special property in the usual lists (prime, square, cube, triangular, Fibonacci, palindrome, perfect), but it is still a composite number.
- 2
18821 is composite. Its prime factorisation is
- 3
The divisors add up to 21600; without 18821 itself that is 2779, so 18821 is deficient (2779 is less than 18821). Euler's totient φ(18821) = 16240 numbers up to 18821 share no factor with it.
- 4
The digits of 18821 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 61 steps to reach 1.
LaTeX source of the formulas on this page
\[ 18821 = 11 \times 29 \times 59 \]
18821 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 8 |
| Sum of divisors | 21600 |
| Euler totient φ(n) | 16240 |
| Square | 354230041 |
| Cube | 6666963601661 |
| Square root | 137.189650 |
| Digit sum / digital root | 20 / 2 |
| Collatz steps to 1 | 61 |
| Scientific notation | 1.8821 × |
18821 in other forms
| Form | Value |
|---|---|
| In words | eighteen thousand eight hundred and twenty-one |
| Binary (base 2) | 100100110000101 |
| Octal (base 8) | 44605 |
| Hexadecimal (base 16) | 4985 |
| Base 3 | 221211002 |
| As time | 18821 seconds = 5 h 13 min 41 s |
Is 18821 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 5) | 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 | Yes (18821 ÷ 11 = 1711) | 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 18821 a prime number?
No. 18821 = 11 × 29 × 59, so it is divisible by 11.
What are the factors of 18821?
1, 11, 29, 59, 319, 649, 1711, 18821.
What is 18821 in binary?
100100110000101 (hexadecimal 4985, octal 44605).
What is the square root of 18821?
About 137.1896.
Is 18821 divisible by 3?
No. Its digits add up to 20, which is not a multiple of 3.
What is special about the number 18821?
It is a composite number with 8 divisors.