https://blog.gongquiz.com/2023/05/22/%eb%8b%a4%ec%9d%8c%ec%9d%80-%ea%b3%84%ec%8a%b9factorial%ec%9d%84-%ea%b5%ac%ed%95%98%ea%b8%b0-%ec%9c%84%ed%95%9c-%ec%84%9c%eb%b8%8c-%ed%94%84%eb%a1%9c%ec%8b%9c%ec%a0%80%ec%9d%b4%eb%8b%a4-%ec%84%9c/