Python program to check if a number is Prime or not

A prime number is a natural number greater than 1 that is not a product of two smaller natural numbers. Any whole number which is greater than 1 and has only two factors that is 1 and the number itself, is called a prime number

Let’s say the following is our input −

7

The output should be as follows −

Prime Number

Check if a number is Prime or not

Let us check if a number if a Prime number or not using the for loop −

Example

# Number to be checked for prime

n = 5

# Check if the number is greater than 1

if n > 1:
	for i in range(2, int(n/2)+1):
		if (n % i) == 0:
			print(num, "is not a prime number")
		break
	else:
		print(n, "is a prime number")
# If the number is less than 1, its also not a prime number.
else:
	print(n, "is not a prime number")

Output

5 is a prime number

Check if a number is Prime or not using sqrt()

Let us check if a number if a Prime number or not using the sqrt() method −

Example

from math import sqrt

# Number to be checked for prime
n = 9

flag = 0

if(n > 1):
	for k in range(2, int(sqrt(n)) + 1):
		if (n % k == 0):
			flag = 1
		break
	if (flag == 0):
		print(n," is a Prime Number!")
	else:
		print(n," is Not a Prime Number!")
else:
	print(n," is Not a Prime Number!")

Output

9 is Not a Prime Number!