20.py

#! /usr/bin/env python

# n! means n x (n - 1) x ... x 3 x 2 x 1
# 
# For example, 10! = 10 x 9 x ... x 3 x 2 x 1 = 3628800,
# and the sum of the digits in the number 10! is 3 + 6 + 2 + 8 + 8 + 0 + 0 = 27.
# 
# Find the sum of the digits in the number 100!


from math import factorial


def sum_digits(n):
    sum = 0

    while n > 0:
        sum += n % 10
        n /= 10

    return sum


print sum_digits(factorial(100))