Prime Number Program in Python (Check Prime or Not)

Numbers have always fascinated humanity, and among them, prime numbers stand out as captivating mathematical entities.

Prime numbers are integers greater than 1 that possess a unique quality – they can only be divided evenly by 1 and themselves, with no other factors in between.

The ways to identify prime numbers has been interesting for mathematicians and programmers alike, leading to the development of efficient algorithms to tackle this timeless challenge.

Here, we will explore the different approaches on how to find prime numbers in Python. We will showcase a variety of programs, providing clear examples, output, and detailed code explanations to simplify the process.

By going through these Python program examples, you will gain a deeper understanding of number divisibility, loops, conditionals, and other fundamental programming concepts in Python. Moreover, you will explore the strengths and weaknesses of different prime checking algorithms, enabling you to make informed decisions when selecting the most suitable approach for your specific requirements.

Prime Number Logic in Python

The logic to check if a number is prime in Python generally involves iterating from 2 to the square root of the number (inclusive) and checking if the number is divisible by any of those values. If it is divisible by any value, then it is not a prime number. Otherwise, it is a prime number.

Here's a step-by-step explanation of the prime number logic in Python:

Start with a number. Let's call it num.
Check if num is less than or equal to 1. If so, it is not a prime number. Return False.
Iterate through numbers from 2 to the square root of num (inclusive). You can use the range function with the appropriate arguments.
For each number i in the range, check if num is divisible by i. If num is divisible by i without a remainder, it means num is not a prime number. Return False.
If the loop completes without finding any factors, it means num is a prime number. Return True.

Let’s dive into the Prime number program in Python!

Prime Number Program in Python

Code

# Simple prime number program in Python using function and for loop

def is_prime(number):
    if number <= 1:
        return False

    for i in range(2, int(number ** 0.5) + 1):
        if number % i == 0:
            return False

    return True

# Example usage
num = int(input("Enter a number: "))

if is_prime(num):
    print(num, "is a prime number.")
else:
    print(num, "is not a prime number.")

Output

Enter a number: 37
37 is a prime number.

Explanation

Here, we defined the is_prime function that takes a number as user input and returns True if it is prime and False otherwise.

To check if a number is prime or not in Python, we follow these steps:

If the number is less than or equal to 1, we immediately return False, as prime numbers are greater than 1.
We use a for loop to iterate from 2 to the square root of the given number (inclusive). We only need to check divisibility up to the square root of the number, as any factors beyond that would already have corresponding factors within the range we check.
For each value of i in the loop, we check if the number is divisible by i. If it is, we return False, indicating that the number is not prime.
If the loop completes without finding any factors, we return True, indicating that the number is prime.

In the example usage section, we prompt the user to enter a number using the input function, convert it to an integer using the int function, and store it in the variable num.

We then call the is_prime function with num as an argument to determine if the number is prime or not. Finally, we display an appropriate message based on the result.

Find Prime Number in Python With User Input

Code

# Python program to check prime number with user input

def is_prime(number):
    if number <= 1:
        return False

    for i in range(2, int(number ** 0.5) + 1):
        if number % i == 0:
            return False

    return True

# Prompt the user to enter a number
num = int(input("Enter a number: "))

if is_prime(num):
    print(num, "is a prime number.")
else:
    print(num, "is not a prime number.")

Output

Enter a number: 34
34 is not a prime number.

Explanation

In this program, we define a function called is_prime that takes a number as input and returns True if it is prime and False otherwise. The implementation of the is_prime function is the same as in the previous examples.
We prompt the user to enter a number using the input function, convert it to an integer using the int function, and store it in the variable num.
Next, we call the is_prime function with num as an argument to determine if the number is prime or not. Finally, we display an appropriate message based on the result.
When you run this program, it will prompt you to enter a number. After you provide the input, it will determine if the number is prime or not and display the result.

Try running this program using the online Python compiler, with different numbers to check if they are prime or not.

Prime Number Program in Python Using while loop

Code

# How to find prime numbers in Python using while loop

def is_prime(number):
    if number <= 1:
        return False

    i = 2
    while i < number:
        if number % i == 0:
            return False
        i += 1

    return True

# Example usage
num = int(input("Enter a number: "))

if is_prime(num):
    print(num, "is a prime number.")
else:
    print(num, "is not a prime number.")

Output

Enter a number: 71
71 is a prime number.

Explanation

We define a function called is_prime that takes a number as input and returns True if it is prime and False otherwise.

To determine if a number is prime or not in Python programming, we follow these steps:

If the number is less than or equal to 1, we immediately return False, as prime numbers are greater than 1.
We initialize i as 2 and start a while loop that continues until i is less than the given number.
Inside the loop, we check if the number is divisible by i. If it is, we return False, indicating that the number is not prime.
If the loop completes without finding any factors, we return True, indicating that the number is prime.
In the example usage section, we prompt the user to enter a number using the input function, convert it to an integer using the int function, and store it in the variable num.
We then call the is_prime function with num as an argument to determine if the number is prime or not. Finally, we display an appropriate message based on the result.

Python Program for Prime Number Using Recursion

Here's an example of a Python program that checks if a number is prime using recursion:

Code

# Check prime number or not using recursion in Python

def is_prime(number, divisor=2):
    if number <= 1:
        return False

    if number == divisor:
        return True

    if number % divisor == 0:
        return False

    return is_prime(number, divisor + 1)

# Example usage
num = int(input("Enter a number: "))

if is_prime(num):
    print(num, "is a prime number.")
else:
    print(num, "is not a prime number.")

Output

Enter a number: 7
7 is a prime number.

Explanation

In this program, we define a recursive function called is_prime that takes a number and a divisor as input. The function checks if the number is prime by recursively dividing it by numbers starting from the given divisor.

The steps involved in the recursive function are as follows:

If the number is less than or equal to 1, we immediately return False, as prime numbers are greater than 1.
If the number is equal to the current divisor, it means that we have checked all possible divisors without finding any factors. In this case, we return True, indicating that the number is prime.
If the number is divisible by the current divisor without a remainder, we return False, indicating that the number is not prime.
Otherwise, we recursively call the is_prime function, incrementing the divisor by 1 in each recursive call.
In the example usage section, we prompt the user to enter a number using the input function, convert it to an integer using the int function, and store it in the variable num.

We then call the is_prime function with num as an argument to determine if the number is prime or not. Finally, we display an appropriate message based on the result.

Python Program to Check Prime Number Between 1 to 100

Code

# Python program to check prime number in given range of 1 to 100

def is_prime(number):
    if number <= 1:
        return False

    for i in range(2, int(number ** 0.5) + 1):
        if number % i == 0:
            return False

    return True

# Iterate through numbers from 1 to 100
for num in range(1, 101):
    if is_prime(num):
        print(num, end=' ')

Output

2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97

Explanation

In this program, we use the is_prime function.

We then iterate through the numbers from 1 to 100 using a for loop. For each number, we call the is_prime function to determine if it is prime. If it is, we print the number on the same line, separated by a space, using the end=' ' parameter in the print function.

When you run this program, it will iterate through the numbers from 1 to 100 and print the prime numbers on a single line, separated by spaces.

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Examples

Prime Number Program in Python (Check Prime or Not)

Prime Number Logic in Python

Prime Number Program in Python

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Output

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Find Prime Number in Python With User Input

Code

Output

Explanation

Prime Number Program in Python Using while loop

Code

Output

Explanation

Python Program for Prime Number Using Recursion

Code

Output

Explanation

Python Program to Check Prime Number Between 1 to 100

Code

Output

Explanation

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Python Program to Check Prime Number : Video