sum of n numbers algorithm code example

Example 1: Determine the sum of al digits of n

def sum_of_digits(n): 
	sum = 0
	while (n != 0): 
		sum = sum + int(n % 10) 
		n = int(n/10) 
	return sum

Example 2: formula for sum of n numbers

Sum of the First n Natural Numbers. We prove the formula 1+ 2+ ... + n = n(n+1) / 2, for n a natural number