Python Program to check if a given number is Prime or not

Program

# Python Program to check if a number is prime or not
inputNum = int(input("Enter a number: "))
if inputNum > 1:   
   for i in range(2,inputNum):
       if (inputNum % i) == 0:
           print(inputNum,"is not a prime number")           
           break
   else:
       print(inputNum,"is a prime number")      
else:
   print(inputNum,"is not a prime number")

This program determines whether a given number is prime. A prime number is a natural number greater than 1 that is divisible only by 1 and itself.

1. Take User Input

   • The program asks the user to enter an integer.

2. Check if Number is Greater than 1

   • Since prime numbers start from 2, numbers ≤1 are not prime.

3. Loop to Check Factors

   • A for loop iterates from 2 to inputNum - 1.
   • If inputNum is divisible by any number in this range, it is not prime, and the loop breaks.

4. Else Clause for Prime Check

   • If the loop completes without finding a factor, the number is prime.

5. Final Output

   • The program prints whether the number is prime or not.

Key Takeaways

• Prime numbers have only two factors: 1 and themselves.
• Composite numbers have additional factors.
• The loop stops early if a factor is found, improving efficiency.

Output 1

$ python3 CheckPrimeNumber.py 
Enter a number: 245
245 is not a prime number

Output 2

$ python3 CheckPrimeNumber.py 
Enter a number: 11
11 is a prime number

Output 3

$ python3 CheckPrimeNumber.py 
Enter a number: 1
1 is not a prime number