def is_prime(n):
    """
    Return True if n is prime, false otherwise.

    >>> is_prime(1)
    False
    >>> is_prime(2)
    True
    >>> is_prime(19)
    True
    """
    if n == 1:
        return False
    i = n - 1

    while i > 1:
        if n % i == 0 or n == 1:
            return False
        i -= 1
    return True