# Different Methods to find Prime Number in Python Program

PythonServer Side ProgrammingProgramming

In this tutorial, we are going to explore different methods to find whether a given number is valid or not. Let's start without further due.

## Method-1

It's a general method to find prime numbers.

• If the number is less than or equal to one, return False.

• If the number is divisible by any number, then the function will return False.

• After the loop, return True.

### Example

Live Demo

# checking for prime
def is_prime(n):
if n <= 1:
return False
else:
for i in range(2, n):
# checking for factor
if n % i == 0:
# return False
return False
# returning True
return True
print(f"Is 2 prime: {is_prime(2)}")
print(f"Is 4 prime: {is_prime(4)}")
print(f"Is 7 prime: {is_prime(7)}")

## Output

If you run the above code, then you will get the following result.

Is 2 prime: True
Is 4 prime: False
Is 7 prime: True

## Method-2

In this method, we are reducing the number of iterations by cutting them to the square root of n.Let's see the code.

### Example

Live Demo

import math
# checking for prime
def is_prime(n):
if n <= 1:
return False
else:
# iterating loop till square root of n
for i in range(2, int(math.sqrt(n)) + 1):
# checking for factor
if n % i == 0:
# return False
return False
# returning True
return True
print(f"Is 2 prime: {is_prime(2)}")
print(f"Is 4 prime: {is_prime(4)}")
print(f"Is 7 prime: {is_prime(7)}")

### Output

If you run the above code, then you will get the following result.

Is 2 prime: True
Is 4 prime: False
Is 7 prime: True

### Method-3

In the previous method, we have checked for the even numbers. We all know that even numbers can't be prime except two. So, in this method, we will remove all evens to reduce the time.

### Example

Live Demo

import math
# checking for prime
def is_prime(n):
# checking for less than 1
if n <= 1:
return False
# checking for 2
elif n == 2:
return True
elif n > 2 and n % 2 == 0:
return False
else:
# iterating loop till square root of n
for i in range(3, int(math.sqrt(n)) + 1, 2):
# checking for factor
if n % i == 0:
# return False
return False
# returning True
return True
print(f"Is 2 prime: {is_prime(2)}")
print(f"Is 4 prime: {is_prime(4)}")
print(f"Is 7 prime: {is_prime(7)}")

## Output

If you run the above code, then you will get the following result.

Is 2 prime: True
Is 4 prime: False
Is 7 prime: True

## Conclusion

If you have doubts in the tutorial, mention them in the comment section.

Published on 24-Apr-2020 16:07:01