Python Program To Check Prime Number : Simple & Efficient Code Examples

In this article, we'll take a look at Hide

1) Algorithm To Check Check Prime Number

In this article, we will create a Python program to check prime number. Before we get started, if you want to Data Type in Python, please go through the following article: Data Types in Python.

A prime number is a positive whole number greater than 1 that is evenly divisible only by 1 and itself. 2, 3, 5, 7, 11, 13 are the first few prime numbers. Some interesting facts about Prime numbers –

2 is the only even prime number
0 and 1 are not considered prime numbers
Numbers that have more than two factors are called composite numbers.
No prime number greater than 5 ends in a 5. Any number greater than 5 that ends in a 5 can be divided by 5.

Algorithm To Check Check Prime Number

Take the input from the User
Check whether the number is greater than 1; if not, then the number is not Prime
Check if the number gets evenly divided by any number from 2 to half of the number
Print the result

Here we have optimized the algorithm to search only till half of the given number, which drastically improves the performance for a very large number.

Python Program to Check Prime Number

# Taking the input from User 
number = int(input("Enter The Number: ")) 

if number > 1: 
    for i in range(2,int(number/2)):
        if (number % i == 0): 
            print(number, "is not a Prime Number") 
            break 
    else: 
        print(number,"is a Prime number") 
        
# If the number is less than 1 it can't be Prime 
else: 
    print(number,"is not a Prime number")

# Taking the input from User

number = int(input("Enter The Number: "))

if number > 1:

for i in range(2,int(number/2)):

if (number % i == 0):

print(number, "is not a Prime Number")

break

else:

print(number,"is a Prime number")

# If the number is less than 1 it can't be Prime

else:

print(number,"is not a Prime number")

Explanation

In the given program, first, we are taking the input from the user using the input keyword and converting it to an integer datatype in case the user inputs a floating number. Next, we are comparing if the number is less than 1 because only a number greater than 1 can be called a Prime number.

Inside the loop, we are dividing the number by every number between 2 and half of the number If no factor is found, the number is Prime and gets printed out along with the number. Running the program for the following test cases gave us the expected result.

Enter The Number: 2
2 is a Prime number

Enter The Number: 11
11 is a Prime number

Enter The Number: 9729262
9729262 is not a Prime Number

Enter The Number: -20
-20 is not a Prime number

Enter The Number: 1
1 is not a Prime number