Python program to check if a number is Prime or not

In this, we’ll write a program that will test if the given number which is greater than 1 is prime or not.

A prime number is a positive integer greater than 1 and which has only two factors 1 & the number itself for example number: 2, 3, 5, 7… etc are prime numbers as they have only two factors .i.e. 1 & the number itself.

# Python program to check if the input number is prime or not
#Take input from the user
num = int(input("Please enter the number: "))
#Check if the given number is greater than 1
if num > 1:
   # Iterate through 2 to num/2.
   for i in range(2,num//2):
      #Select if the number is divisible by any number between 2 and num/2.
      if (num % i) == 0:
         print(num,"is not a prime number")
         print(i,"times",num//i,"is",num)
         break
      else:
         #If given number is not fully divisible by any number between 1 and num/2, then its prime.
         print(num,"is a prime number")
# Also, if the number is less than 1, its also not a prime number.
else:
   print(num,"is not a prime number")

Output

Please enter the number: 47
47 is a prime number
>>>
================= RESTART: C:/Python/Python361/primeNum1.py =================
Please enter the number: -2
-2 is not a prime number
>>>
================= RESTART: C:/Python/Python361/primeNum1.py =================
Please enter the number: 3333
3333 is not a prime number
3 times 1111 is 3333

User-Input 1: num: 47

Output: Number(47) is a prime number

User-Input 2: num = -2

Output: Number(-2) is not a prime number

User-Input 3: num = 3333

Output: Number(3333) is not a prime number

In the above program, we check if the user input number is prime or not. Because numbers less than or equal to 1 are not prime numbers, therefore we only consider user-input greater than 1.

Then we check if the user-input is exactly divisible by any number between 2 to user-input/2. If we find a factor in that range, the number is not a prime number else, it’s a prime number.

Samual Sam

Published on 19-Feb-2019 12:26:05

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