The number 25
25 is a perfect square (5²). Its prime factorisation is . Divisors (3): 1, 5, 25.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 25: a perfect square (5²); the square of a prime (5²).
- 2
25 is composite. Its prime factorisation is
- 3
The divisors add up to 31; without 25 itself that is 6, so 25 is deficient (6 is less than 25). Euler's totient φ(25) = 20 numbers up to 25 share no factor with it.
- 4
The digits of 25 add up to 7, and repeating that until one digit is left gives the digital root 7. The Collatz sequence (halve if even, else 3n+1) takes 23 steps to reach 1.
LaTeX source of the formulas on this page
\[ 25 = 5^{2} \]25 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 3 |
| Sum of divisors | 31 |
| Euler totient φ(n) | 20 |
| Square | 625 |
| Cube | 15625 |
| Square root | 5 |
| Digit sum / digital root | 7 / 7 |
| Collatz steps to 1 | 23 |
| Scientific notation | 2.5 × |
| Perfect power |
25 in other forms
| Form | Value |
|---|---|
| In words | twenty-five |
| Roman numerals | XXV |
| Binary (base 2) | 11001 |
| Octal (base 8) | 31 |
| Hexadecimal (base 16) | 19 |
| Base 3 | 221 |
| As time | 25 seconds |
Is 25 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 (25 ÷ 5 = 5) | 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 7) | 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 3) | 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 25 a prime number?
No. 25 = , so it is divisible by 5.
What are the factors of 25?
1, 5, 25.
What is 25 in binary?
11001 (hexadecimal 19, octal 31).
What is the square root of 25?
5, because 5 × 5 = 25.
What is 25 in Roman numerals?
XXV.
Is 25 divisible by 3?
No. Its digits add up to 7, which is not a multiple of 3.
What is special about the number 25?
25 is a perfect square (5²); the square of a prime (5²).