https://qiita.com/drken/items/dc53c683d6de8aeacf5a
https://triple-four.hatenablog.com/entry/2019/02/05/190512
https://qiita.com/drken/items/23a4f604fa3f505dd5ad
https://note.nkmk.me/python-math-factorial-permutations-combinations/
http://sevendays-study.com/algorithm/ex-day4.html