Python program to check prime number

Description: Write a Python program to check whether a number is prime.

Rules and hints:

• A prime number is greater than 1 and has no divisor other than 1 and itself.
• You only need to test divisors up to the square root of the number.

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Python program to check a prime number

def is_prime(n):
    if n < 2:
        return False
    for i in range(2, int(n ** 0.5) + 1):
        if n % i == 0:
            return False
    return True

for n in (2, 15, 17, 1):
    if is_prime(n):
        print(n, "is prime")
    else:
        print(n, "is not prime")

Output:

How it works

• Numbers below 2 are not prime.
• For 15 the loop tests 2 and 3. Since 15 % 3 == 0, it returns False.
• For 17 the loop tests 2, 3 and 4. None divides it, so it is prime.
• As soon as one divisor is found, return False ends the function early.

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