The number 21825
21825 is a composite number with 18 divisors. Its prime factorisation is × × 97. Divisors (18): 1, 3, 5, 9, 15, 25, 45, 75, 97, 225, 291, 485, 873, 1455, 2425, 4365 … 21825.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
21825 has no famous special property in the usual lists (prime, square, cube, triangular, Fibonacci, palindrome, perfect), but it is still a composite number.
- 2
21825 is composite. Its prime factorisation is
- 3
The divisors add up to 39494; without 21825 itself that is 17669, so 21825 is deficient (17669 is less than 21825). Euler's totient φ(21825) = 11520 numbers up to 21825 share no factor with it.
- 4
The digits of 21825 add up to 18, and repeating that until one digit is left gives the digital root 9. The Collatz sequence (halve if even, else 3n+1) takes 69 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21825 = 3^{2} \times 5^{2} \times 97 \]21825 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 18 |
| Sum of divisors | 39494 |
| Euler totient φ(n) | 11520 |
| Square | 476330625 |
| Cube | 10395915890625 |
| Square root | 147.732867 (= 15√97) |
| Digit sum / digital root | 18 / 9 |
| Collatz steps to 1 | 69 |
| Scientific notation | 2.1825 × |
21825 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand eight hundred and twenty-five |
| Binary (base 2) | 101010101000001 |
| Octal (base 8) | 52501 |
| Hexadecimal (base 16) | 5541 |
| Base 3 | 1002221100 |
| As time | 21825 seconds = 6 h 3 min 45 s |
Is 21825 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 (21825 ÷ 3 = 7275) | 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 | Yes (21825 ÷ 5 = 4365) | 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 6) | 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 1) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | Yes (21825 ÷ 9 = 2425) | A number is divisible by 9 if the digits add up to a multiple of 9. |
| 10 | No (remainder 5) | 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 21825 a prime number?
No. 21825 = × × 97, so it is divisible by 3.
What are the factors of 21825?
1, 3, 5, 9, 15, 25, 45, 75, 97, 225, 291, 485, 873, 1455, 2425, 4365, 7275, 21825.
What is 21825 in binary?
101010101000001 (hexadecimal 5541, octal 52501).
What is the square root of 21825?
About 147.7329, exactly 15√97.
Is 21825 divisible by 3?
Yes. Its digits add up to 18, a multiple of 3.
What is special about the number 21825?
It is a composite number with 18 divisors.