input: Write a function to demonstrate the concept of recursion in Python by calculating the factorial of a given number. The function should return the factorial of the number if it is greater than or equal to 1, otherwise it should return 1.
  
  def factorial(n):
     if n == 1:
        return 1
     else:
        return n * factorial(n - 1)
  
  assert factorial(5) == 120
  assert factorial(1) == 1
  assert factorial(3) == 6
  assert factorial(0) == 1
  assert factorial(4) == 24
output: def factorial(n):
     if n == 0 or n == 1:
        return 1
     else:
        return n * factorial(n - 1)