The number 21800
21800 is a composite number with 24 divisors. Its prime factorisation is × × 109. Divisors (24): 1, 2, 4, 5, 8, 10, 20, 25, 40, 50, 100, 109, 200, 218, 436, 545 … 21800.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
21800 has no famous special property in the usual lists (prime, square, cube, triangular, Fibonacci, palindrome, perfect), but it is still a composite number.
- 2
21800 is composite. Its prime factorisation is
- 3
The divisors add up to 51150; without 21800 itself that is 29350, so 21800 is abundant (29350 is more than 21800). Euler's totient φ(21800) = 8640 numbers up to 21800 share no factor with it.
- 4
The digits of 21800 add up to 11, and repeating that until one digit is left gives the digital root 2. The Collatz sequence (halve if even, else 3n+1) takes 69 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21800 = 2^{3} \times 5^{2} \times 109 \]21800 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 24 |
| Sum of divisors | 51150 |
| Euler totient φ(n) | 8640 |
| Square | 475240000 |
| Cube | 10360232000000 |
| Square root | 147.648231 (= 10√218) |
| Digit sum / digital root | 11 / 2 |
| Collatz steps to 1 | 69 |
| Scientific notation | 2.18 × |
21800 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand eight hundred |
| Binary (base 2) | 101010100101000 |
| Octal (base 8) | 52450 |
| Hexadecimal (base 16) | 5528 |
| Base 3 | 1002220102 |
| As time | 21800 seconds = 6 h 3 min 20 s |
Is 21800 divisible by 2 to 12?
| Divisor | Answer | Rule |
|---|---|---|
| 2 | Yes (21800 ÷ 2 = 10900) | 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 | Yes (21800 ÷ 4 = 5450) | A number is divisible by 4 if the last two digits make a multiple of 4. |
| 5 | Yes (21800 ÷ 5 = 4360) | A number is divisible by 5 if the last digit is 0 or 5. |
| 6 | No (remainder 2) | 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 | Yes (21800 ÷ 8 = 2725) | 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 | Yes (21800 ÷ 10 = 2180) | A number is divisible by 10 if the last digit is 0. |
| 11 | No (remainder 9) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 8) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 21800 a prime number?
No. 21800 = × × 109, so it is divisible by 2.
What are the factors of 21800?
1, 2, 4, 5, 8, 10, 20, 25, 40, 50, 100, 109, 200, 218, 436, 545, 872, 1090, 2180, 2725, 4360, 5450, 10900, 21800.
What is 21800 in binary?
101010100101000 (hexadecimal 5528, octal 52450).
What is the square root of 21800?
About 147.6482, exactly 10√218.
Is 21800 divisible by 3?
No. Its digits add up to 11, which is not a multiple of 3.
What is special about the number 21800?
It is a composite number with 24 divisors.