calculate factorial in python : Instead of calculating a factorial one digit at a time, use this calculator to calculate the factorial n! of a number n. Enter an integer, up to 4 digits long. You will get the long integer answer and also the scientific notation for large factorials. You may want to copy the long integer answer result and paste it into another document to view it.

### What Is Factorial?

A number’s factorial is the function that multiplies the number by each natural number below it. Factorial can be expressed symbolically as “!” As a result, n factorial is the product of the first n natural numbers and is denoted by n!

#### calculate factorial

Example : Factorial of 5!

5*4*3*2*1 = 120

### Formula to calculate n factorial

The formula for n factorial is:n!=n×(n−1)!n!=n×(n−1)!

There are n! methods to arrange n items in succession in mathematics. “The factorial n! indicates the number of permutations of n things.” [1] As an example:

What about the number “0!”

The Zero Factorial is intriguing… it is widely accepted that 0! Equals 1.

It may appear strange that multiplying no numbers results in one, but follow the process backwards from, say, 4! such as this:

We can use the same formula to calculate the factorial of number in python

To understand this example, you need be familiar with the following Python programming concepts:

if…else in Python Statement

Python for Loop

Recursion in Python

Let Start with the For Loop

## calculate factorial in python using For Loop

```
number = int(input("Enter a factorial number: "))
fact = 1
if number < 0:
print(" Factorial does not exist for negative numbers")
elseif number == 0:
print("The factorial of 0 is 1")
else:
for i in range(1,num + 1):
fact = fact*i
print("The factorial of",num,"is",fact)
```

The number whose factorial is to be calculated is stored in num, and we use the if…elif…else expression to verify if the value is negative, zero, or positive. If the integer is positive, we calculate the factorial using the for loop and range() function.

#### OUTPUT

```
Enter a number: 5
The factorial of 5 is 120
```

Factorial using Recursion

```
import math
def fact(x):
if x == 1:
return 1
else:
# recursive call to the function
return (x * fact(x-1))
number = int(input("Enter the Factotrial number:"))
facto = fact(number)
print("Factorial of", number, "is", facto)
```

OUTPUT

```
Enter a number: 5
The factorial of 5 is 120
```

factorial() is a recursive function that calls itself in the example above. By decreasing the value of x, the function will recursively call itself.