https://blog.csdn.net/liu_jiangwen/article/details/81387036
差分序列
https://riteme.github.io/blog/2016-11-29/delta-and-stirling.html#_7
https://blog.csdn.net/liangzhaoyang1/article/details/53145994
https://blog.csdn.net/liu_jiangwen/article/details/81387036
差分序列
https://riteme.github.io/blog/2016-11-29/delta-and-stirling.html#_7