Write a function `is_prime(n: int) -> bool` that determines whether a given integer `n` is a prime number. A prime number is a natural number greater than 1 that has no positive divisors other than 1 and itself.
#### Example Usage
```python [main.nopy]
print(is_prime(2)) # True
print(is_prime(4)) # False
print(is_prime(13)) # True
print(is_prime(1)) # False
print(is_prime(-5)) # False
```
#### Constraints
- The input will always be an integer.
- The function should return `True` if the number is prime, otherwise `False`.