INTRODUCTION

A prime number is a number which has only two factors. It can only be divided by 1 and itself.

• Numbers 0 and 1 are not prime numbers.
• Decimals (not whole numbers) like 3.67 are not prime numbers.
• Negative numbers are not prime numbers.

EXAMPLES

1) Factors of number 25: 

$F_{25}=\{1, 5, 25\}$

Number 25 has 3 factors so 25 is not a prime number.

2) Factors of number 29: 

$F_{29}=\{1, 29\}$

Number 29 has 2 factors so 29 is a prime number.

Sometimes the definition of prime number says that it’s a number which is divisible by 1 and itself. In that way number 1 is a prime number.

PYTHON CODE

num = float(input("Enter a number: "))

if num.is_integer():
   if num > 0:
      if num == 1:
         print("1 is considered a prime number by some definitions.")
      else:
         is_prime = True
         if num > 1:
             for i in range(2,int(num)):
                 if (num % i) == 0:
                     is_prime = False
                     break
         if is_prime:
            print(num, "is a prime number")
         else:
            print(num, "is not a prime number")
   elif num == 0:
      print("0 is not considered a prime number.")
   else:
      print("Negative numbers are not considered prime.")
else:
   print("Decimal numbers are not considered prime.")

⬆️⬆️⬆️ See in Google Colaboratory

HOW THE CODE WORKS?

1. The program asks the user to enter the number and checks if the entered number is an integer (methodis_integer()).
2. If the number entered is not an integer, the program displays an appropriate message and exits.If the number entered is an integer, the program checks whether it is positive.
3. If the entered number is less than or equal to 0, the program displays an appropriate message and exits.If the entered number is greater than 0, the program checks whether it is 1.
4. If the entered number is equal to 1, the program displays an appropriate message.If the number entered is greater than 1, the program initializes the variableis_prime as True.
5. The program checks whether a number is prime by traversing all possible divisors.
6. If a divisor is found, the program sets the variableis_prime as False and breaks the loop.
7. The program displays a message indicating whether the entered number is a prime number.