Function is_safe_prime

maths/germain_primes.py:41–66

Checks if input number and (number - 1)/2 are prime. The smallest safe prime is 5, with the Germain prime is 2. >>> is_safe_prime(5) True >>> is_safe_prime(11) True >>> is_safe_prime(1) False >>> is_safe_prime(2) False >>> is_safe_prime(3) False >>> i

(number: int)

def is_safe_prime(number: int) -> bool:
    """Checks if input number and (number - 1)/2 are prime.
    The smallest safe prime is 5, with the Germain prime is 2.

    >>> is_safe_prime(5)
    True
    >>> is_safe_prime(11)
    True
    >>> is_safe_prime(1)
    False
    >>> is_safe_prime(2)
    False
    >>> is_safe_prime(3)
    False
    >>> is_safe_prime(47)
    True
    >>> is_safe_prime('abc')
    Traceback (most recent call last):
        ...
    TypeError: Input value must be a positive integer. Input value: abc
    """
    if not isinstance(number, int) or number < 1:
        msg = f"Input value must be a positive integer. Input value: {number}"
        raise TypeError(msg)

    return (number - 1) % 2 == 0 and is_prime(number) and is_prime((number - 1) // 2)


if __name__ == "__main__":