Write a function to check if a number is prime. with explanation

Question

Anubhav Kumar · Answer

Prime Number Reminder:
A prime number is a number greater than 1 that has
no divisors other than 1 and itself.Examples: 2, 3, 5, 7, 11, 13 are prime.4, 6, 8, 9, 10 are not prime because they can be divided by numbers other than 1 and themselves.
Python Program
def is_prime_number(n):
    # Prime numbers are greater than 1
    if n andlt;= 1:
        return False
    # Check divisibility from 2 to sqrt(n) -andgt; (n**0.5)
    for i in range(2, int(n**0.5) + 1):
        if n % i == 0:  # if divisible by i
            return False
    return True
# Test the function
num = int(input("Enter a number: "))
if is_prime_number(num):
    print(num, "is a prime number")
else:
    print(num, "is not a prime number")
Explanation
Base Case:
Numbers 0, 1, and negative numbers are not prime.
if n andlt;= 1:
    return False
Check divisibility:
for i in range(2, int(n**0.5) + 1):
We only check divisors up to √n instead of n-1.Why? If n has a factor larger than √n, then the corresponding smaller factor would already have been found.This makes it efficient.
Check modulus:
if n % i == 0:
    return False
If n divides evenly by i, then it’s not prime.
Return True if no divisors found:
return True
and 
Output :
Enter a number: 29
29 is a prime number
Enter a number: 20
20 is not a prime number

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Write a function to check if a number is prime. with explanation

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Prime Number Reminder:

Python Program

Explanation

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