https://www.cnblogs.com/mjtcn/p/9754334.html
https://www.lydsy.com/JudgeOnline/problem.php?id=1257
https://www.cnblogs.com/mjtcn/p/8982006.html
数论必刷题
原文：https://www.cnblogs.com/Dxy0310/p/9800636.html
