Project Euler

Problem

This problem comes from Project Euler 20

Problem

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

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

Another simple problem.

1. Calculate $100!$
2. Convert the number into a string
3. Iterate over the string and convert into a number array
4. Sum the array

Code

# Project Euler: Problem 20
# Factorial digit sum

from math import factorial as f

number = f(100)
number_list = [int(i) for i in str(number)]
print(sum(number_list))