# Project Euler Problem 20: Factorial Digit Sum¶

The source code for this problem can be found here.

## Problem Statement¶

$$n!$$ means $$n \times (n - 1) \times \dots \times 3 \times 2 \times 1$$

For example, $$10! = 10 \times 9 \times \dots \times 3 \times 2 \times 1 = 3628800$$,
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 $$100!$$

## Solution Discussion¶

Build the value of $$100!$$ using Python’s arbitrary precision arithmetic and then perform a decimal digit sum on that result.

## Solution Implementation¶

from lib.digital import digit_sum
from lib.sequence import Factorials

def solve():
""" Compute the answer to Project Euler's problem #20 """
target = 100
factorials = Factorials()
x = factorials[target]

solutions.problem20.solve()