# Python factorial Program Example

In the Python example series, we will discuss the Python Factorial Program.

What is factorial of a number?

First understand what is factorial of a number. Factorial of number n is the multiplication of n with its previous number up to 1 like

n*(n-1) *(n-2) *(n-3) …*1

e.g. if n is 5 then factorial of 5 will be 5*4*3*2*1 which is 120.

Some point to remember about factorial

• 0 factorial is 1
• 1 factorial is also 1

Example

Let’s understand factorial program by example

```# Python factorial example
# 0! is 1
# 1! is 1

n=input("Enter the number:")
n=int(n)

#check whether number is 0 or 1
f=1
if n==0 or n==1 :
print("factorial of", n,"is:", f)

else :
for i in range(1,n + 1):
f = f*i

print("The factorial of",n,"is",f)

```

Output

```Enter the number:5

The factorial of 5 is 120```

Explanation:

• In above example, we ask the user to enter the number.
• We check whether entered number is 0 or 1, if number is 0 or 1, factorial of number will be 1, as we know that factorial of 0 and 1 is 1.
• If number is not 0 or 1, then program will go into else part.
• In else part, for i in range (1, n + 1), we have range function which will start from 1 and go to n+1 i.e. 6, as range function will take the number between 1 to 6. i.e. 1 to 5, so for loop will start from 1 and run till 5.
• In the next step, f = f*I, we are multiply current number with previous calculated number.
• At the end, we print the factorial of number.