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Functions / Factorial 


						
								

			

			


	







	
			

			

				
Factorial
 

   
The definition of the factorial number is that 0! is 1, and n! = n(n-1)!


 
# Factorial definition: 
# 
# 0! is 1
# n! = n(n-1)!
#
# 3! is 3 times 2!, which is 2 times 1!, which is 1 times 0!.
# 3! = 3 * 2! = 3 * 2 * 1! = 3 * 2 * 1 * 0! = 6

def factorial(n):
    
    if (n == 0): return 1

    n = n * factorial(n-1)
    return n

assert factorial(3) == 6
assert factorial(0) == 1
assert factorial(4) == 24




Fibonacci
 

  
Each number is the sum of the two preceding ones.


 
# Fibonacci sequence:
#
#    fb(0) = 0
#    fb(1) = 1
#    fb(n) = fb(n-1) + fb(n-2)
#
# Each number is the sum of the two preceding ones.

def fibonacci(n):

    if (n==0): return 0
    if (n==1): return 1

    return fibonacci(n-1) + fibonacci(n-2)

assert fibonacci(0) == 0
assert fibonacci(1) == 1
assert fibonacci(2) == 1
assert fibonacci(3) == 2
assert fibonacci(4) == 3
assert fibonacci(5) == 5





			
					

			

		

	

	
	

	


				
		

		
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