In this post, We will be going to see different ways to write a code in Python for checking whether a number is Prime or not, provided number > 1.

**Prime Number** is a natural number which is greater than 1 and that has no positive divisors other than 1 and number itself.

**Examples : **

Input:n = 17Output:17 is a Prime NumberInput:n = 21Output:17 is not a Prime Number

**Code 1:** Run the loop from 1 to the given number and count the factors if factors are greater than 2 then it is not a prime otherwise prime.

# input number number = 17 # maxCount variable set to 2 # because prime numbers # have only 2 divisors # i.e. 1 and itself maxCount = 2 # initialise a variable count = 0 # loop from 1 to number for i in range(1, number + 1) : # if number is divisible by any # number (i) then increment # count variable by 1 if number % i == 0 : count += 1 # if value of count is greater than # maxCount value then number is not # prime otherwise prime if count > maxCount : print(number,"is not a Prime Number") else: print(number,"is a Prime Number")

**Output :**

17 is a Prime Number

**Code 2:** Run the loop from 2 to half of its number if any number in between divides the given number then the given number is not a prime otherwise prime.

# input number and flag assignment # in one line number, flag = 17, 0 # loop from 2 to half of the # given number for i in range(2, number // 2 + 1) : # if number is divisible by any # number (i) in b/w 2 to half of # its number then set falg to 1 # and break out of the loop if number % i == 0 : flag = 1 break # if flag is 1 then # number is not prime # otherwise prime if flag : print(number,"is not a Prime Number") else: print(number,"is a Prime Number")

**Output :**

17 is a Prime Number

**Code 3:** Use the concept of **for-else** loop.

# input number number = 17 # loop from 2 to half of the # given number for i in range(2, number // 2 + 1) : # if number is divisible by any # number (i) in b/w 2 to half of # its number then it is not # a prime number if number % i == 0 : print(number,"is not a Prime Number") break # if not divisible then it is # a prime number else : print(number,"is a Prime Number")

**Output :**

17 is a Prime Number

**Code 4:**

# main code if __name__ == "__main__" : # input number number = 17 # loop from 2 to half of the # given number for i in range(2, number // 2 + 1) : # if number is divisible by any # number (i) in b/w 2 to half of # its number then it is not # a prime number if number % i == 0 : print(number,"is not a Prime Number") break # if not divisible then it is # a prime number else : print(number,"is a Prime Number")

**Output :**

17 is a Prime Number

**Code 5:** Create a user defined function for checking number is prime or not.

# define a user defined # function for checking # a number is prime or # not def checkPrime(number) : # loop from 2 to half of the # given number for i in range(2, number // 2 + 1) : # if number is divisible by any # number (i) in b/w 2 to half of # its number then it is not # a prime number if number % i == 0 : print(number,"is not a Prime Number") break # if not divisible then it is # a prime number else : print(number,"is a Prime Number") # main code if __name__ == "__main__" : # input number number = 17 # function calling checkPrime(number)

**Output :**

17 is a Prime Number