The number 5
5 is a Fibonacci number, a twin prime (3 and 5 are both prime) and the 3rd prime number. Its only divisors are 1 and 5.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 5: a Fibonacci number; a twin prime (3 and 5 are both prime); the 3rd prime number; a binary palindrome (101).
- 2
5 is prime, so its only factors are 1 and 5. It is the 3rd prime; the next prime is 7 and the one before is 3.
- 3
The divisors add up to 6; without 5 itself that is 1, so 5 is deficient (1 is less than 5). Euler's totient φ(5) = 4 numbers up to 5 share no factor with it.
- 4
The digits of 5 add up to 5, and repeating that until one digit is left gives the digital root 5. The Collatz sequence (halve if even, else 3n+1) takes 5 steps to reach 1.
5 at a glance
| Property | Value |
|---|---|
| Type | prime |
| Number of divisors | 2 |
| Sum of divisors | 6 |
| Euler totient φ(n) | 4 |
| Square | 25 |
| Cube | 125 |
| Square root | 2.236068 |
| Digit sum / digital root | 5 / 5 |
| Collatz steps to 1 | 5 |
| Scientific notation | 5 × |
5 in other forms
| Form | Value |
|---|---|
| In words | five |
| Roman numerals | V |
| Binary (base 2) | 101 |
| Octal (base 8) | 5 |
| Hexadecimal (base 16) | 5 |
| Base 3 | 12 |
| As time | 5 seconds |
Is 5 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 | Yes (5 ÷ 5 = 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 5) | 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 5) | 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 5 a prime number?
Yes. 5 is divisible only by 1 and itself.
What are the factors of 5?
1, 5.
What is 5 in binary?
101 (hexadecimal 5, octal 5).
What is the square root of 5?
About 2.2361.
What is 5 in Roman numerals?
V.
Is 5 divisible by 3?
No. Its digits add up to 5, which is not a multiple of 3.
What is special about the number 5?
5 is a Fibonacci number; a twin prime (3 and 5 are both prime); the 3rd prime number; a binary palindrome (101).