How to Find Prime Numbers Using Python

Prime numbers are an important concept in programming and mathematics. In this blog, we will learn how to check whether a number is prime using a simple Python program.

What is a Prime Number?

A prime number is a number that has only two factors:

• 1
• The number itself

For example:

2, 3, 5, 7, 11, 13, 17, 19

are prime numbers.

But 4 is not prime because it can be divided by 1, 2, and 4.

Python Program

def prime(n):
    for i in range(2, n):
        if n % i == 0:
            return False
    return True

for n in range(10, 21):
    if prime(n):
        print(n)

How Does the Program Work?

1. Create a function

def prime(n):

This creates a function called prime() that takes a number n.

2. Check numbers from 2

for i in range(2, n):

The loop checks numbers starting from 2 up to n - 1.

3. Check divisibility

if n % i == 0:

The % operator gives the remainder.

If the remainder is 0, the number can be divided exactly by i.

So, the number is not prime.

4. Return False

return False

If a divisor is found, the function returns False.

5. Return True

return True

If no divisor is found, the number is prime, so the function returns True.

6. Check numbers from 10 to 20

for n in range(10, 21):

This checks every number from 10 to 20.

7. Print prime numbers

if prime(n):
    print(n)

If the number is prime, it will be printed.

Output

11
13
17
19

Conclusion

Finding prime numbers is a good beginner programming exercise. It helps us understand:

• Functions
• for loops
• if conditions
• The % operator
• return statements