# Python Function to check Prime Number

In this example, we will learn whether the entered number is a prime number or not using a user-defined function.
A prime number is a number that is divisible by 1 and itself. The same principle we are going to explore in this example.

## Python Function to check the primary number [ Old method ]

```def check_prime(n):
flag = True
for x in range(2, n//2):
if n % x == 0:
flag = False

return flag

if __name__ == "__main__":
n = int(input('Enter any integer number  : '))
result = check_prime(n)
print("Prime Number " if (result) else '"Not prime Number')
```

Output of the above python program

```rakesh@folio MINGW64 /e/python (master)
\$ python -u "e:\python\functions\check_prime.py"
Enter any integer number  : 16
"Not prime Number

rakesh@folio MINGW64 /e/python (master)
\$ python -u "e:\python\functions\check_prime.py"
Enter any integer number  : 17
Prime Number

rakesh@folio MINGW64 /e/python (master)
\$ python -u "e:\python\functions\check_prime.py"
Enter any integer number  : 1
Prime Number

rakesh@folio MINGW64 /e/python (master)
\$ python -u "e:\python\functions\check_prime.py"
Enter any integer number  : 2
Prime Number
```

## A second and Most efficient method to check prime Number

```from math import sqrt
def prime_number(n):
flag = True
for x in range(2, int(sqrt(n))+1):
if n % x == 0:
flag = False
return flag
```

Implementation of the above function to check Prime number. The above function tried to divide all the number between 2 and sqrt( ) of the number and this is the shortest method to check prime number.

```if __name__ == "__main__":
if(prime_number(12)):
print('Prime Number')
else:
print('Not a prime Number')
```

The same function can be used to find out the prime number between two numbers.