Prime Number Program Using Function in Python

A prime number is a number greater than 1 that has only two factors: 1 and itself.

Examples of prime numbers are 2, 3, 5, 7, 11, 13, 17, and 19.

In Python, we can use a function to check whether a number is prime.

Python Program

def is_prime(n):
    if n < 2:
        return False

    for i in range(2, n):
        if n % i == 0:
            return False

    return True


number = int(input("Enter a number: "))

if is_prime(number):
    print(number, "is a prime number")
else:
    print(number, "is not a prime number")

How It Works

1. Create a function

def is_prime(n):

The function is_prime() receives a number n.

2. Check numbers less than 2

if n < 2:
    return False

Numbers like 0 and 1 are not prime numbers.

3. Check for factors

for i in range(2, n):

The loop checks numbers from 2 up to n-1.

4. Use the modulo operator

if n % i == 0:
    return False

If n is exactly divisible by any number other than 1 and itself, it is not prime.

5. Return True

return True

If no factor is found, the number is prime.

Example Output

Enter a number: 17
17 is a prime number

Another example:

Enter a number: 20
20 is not a prime number

Conclusion

Using a function makes the prime number program simple, reusable, and easy to understand. The same is_prime() function can also be used when checking many numbers in a program.