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Check if a number is Prime

ICSM Computer 1596 08-Sep-2025

Check if a number is Prime with example and code.

python-3.4 Python 3

Updated on 09-Sep-2025

ICSM Computer

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Anubhav Kumar

08-Sep-2025

def is_prime(n):
    # 1. Prime numbers are greater than 1
    if n < 2:
        return False
    
    # 2. Loop from 2 up to √n (square root of n)
    #    If a number has a divisor larger than its square root,
    #    the matching smaller divisor would already be found.
    for i in range(2, int(n**0.5) + 1):
        # 3. If n is divisible by i, then it's not a prime
        if n % i == 0:
            return False
    
    # 4. If no divisors were found, n is prime
    return True


# Test the function
print(is_prime(17))  # True → 17 is a prime number
print(is_prime(18))  # False → 18 is divisible by 2, 3, 6, 9

Answer:

17 → True
18 → False

Explanation:

Prime means divisible only by 1 and itself.
We only check up to sqrt(n) for efficiency.

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Check if a number is Prime

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