A number is prime if it is greater than 1 and has no divisors other than 1 and itself.

Code Example:

def is_prime(n):
    return len([x for x in range(2, int(n ** 0.5) + 1) if n % x == 0]) == 0

print(is_prime(11))  # Output: True
print(is_prime(4))   # Output: False

This function uses a list comprehension to check for factors of $n$ up to its square root and determines if $n$ is prime.