euler_20.py

#!/usr/bin/env python3

'''
Factorial digit sum
Problem 20

n! means n × (n − 1) × ... × 3 × 2 × 1

For example, 10! = 10 × 9 × ... × 3 × 2 × 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!
'''

factorial = 1
answer = 0

for n in range(1, 100):
    factorial *= n

for i in str(factorial):
    answer += int(i)

print(answer)