In this Python program, we will learn how to find the factorial of a number.

In mathematics, the factorial of a positive integer n, denoted by n! is the product of all positive integers less than or equal to n:

n!=(n-1)x(n-2)x(n-3)x….3x2x1

The factorial, symbolized by an exclamation mark (!), is a quantity defined for all integers greater than or equal to 0.

For example,

5!=5x4x3x2x1=120

6!=6x5x4x3x2x1=720

The value of 0! is 1.

Here is the source code to find the factorial of a number.

```
# Python Program to Find the Factorial of a Number
# To take input from the user
num = int(input("Enter a number: "))
factorial = 1
# check if the number is negative, positive or zero
if num < 0:
print("Sorry, factorial does not exist for negative numbers")
elif num == 0:
print("The factorial of 0 is 1")
else:
for i in range(1,num + 1):
factorial = factorial*i
print("The factorial of",num,"is",factorial)
```

Enter a number: 5

The factorial of 5 is 120

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