The number 21025
21025 is a perfect square (145²). Its prime factorisation is × . Divisors (9): 1, 5, 25, 29, 145, 725, 841, 4205, 21025.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21025: a perfect square (145²).
- 2
21025 is composite. Its prime factorisation is
- 3
The divisors add up to 27001; without 21025 itself that is 5976, so 21025 is deficient (5976 is less than 21025). Euler's totient φ(21025) = 16240 numbers up to 21025 share no factor with it.
- 4
The digits of 21025 add up to 10, and repeating that until one digit is left gives the digital root 1. The Collatz sequence (halve if even, else 3n+1) takes 87 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21025 = 5^{2} \times 29^{2} \]21025 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 9 |
| Sum of divisors | 27001 |
| Euler totient φ(n) | 16240 |
| Square | 442050625 |
| Cube | 9294114390625 |
| Square root | 145 |
| Digit sum / digital root | 10 / 1 |
| Collatz steps to 1 | 87 |
| Scientific notation | 2.1025 × |
| Perfect power |
21025 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand and twenty-five |
| Binary (base 2) | 101001000100001 |
| Octal (base 8) | 51041 |
| Hexadecimal (base 16) | 5221 |
| Base 3 | 1001211201 |
| As time | 21025 seconds = 5 h 50 min 25 s |
Is 21025 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 | Yes (21025 ÷ 5 = 4205) | 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 | No (remainder 4) | 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 | No (remainder 1) | 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 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 21025 a prime number?
No. 21025 = × , so it is divisible by 5.
What are the factors of 21025?
1, 5, 25, 29, 145, 725, 841, 4205, 21025.
What is 21025 in binary?
101001000100001 (hexadecimal 5221, octal 51041).
What is the square root of 21025?
145, because 145 × 145 = 21025.
Is 21025 divisible by 3?
No. Its digits add up to 10, which is not a multiple of 3.
What is special about the number 21025?
21025 is a perfect square (145²).