write a recursive function to find factorial of a number.

Sure, here is a simple recursive function in Python to find the factorial of a number:

def factorial(n):
    # Base case: factorial of 0 is 1
    if n == 0:
        return 1
    # Recursive case: n! = n * (n-1)!
    else:
        return n * factorial(n-1)

This function works by defining the base case as the factorial of 0 being 1. Then, for any other number n, it recursively calls itself with the argument n-1, until it eventually reaches the base case. The result is the product of all integers from n down to 1.