做个备忘录把……
令\(f_i\)表示至少选择\(i\)个，\(g_i\)表示敲好选择\(i\)个
\(f_i=\sum_{j=0}^i \dbinom{n}{j}*g_j\)
\(g_i=\sum_{j=0}^{i}(-1)^{i-j}\dbinom {n}{j}f_j\)
\(\dbinom{n}{k}=\sum_{i=0}^k\dbinom{m}{i}*\dbinom{k-i}{n-m}\)
\(\dbinom{m}{i}*\dbinom{i}{j}=\dbinom{m}{i}*\dbinom{m-j}{i-j}\)
\(M_i=lcm/m_i, x_i=M_i^{-1}(mod\ m_i)\)
\(Ans=\sum_{i=1}^n x_i*a_i*M_i(mod\ lcm)\)
\(S(n, m)=\dfrac{1}{m!}*\sum_{k=0}^m(-1)^k*\dbinom{m}{l}*(m-k)^n\)
\(n^k=\sum_{i=0}^kS(k, i) * i! *\dbinom{n}{i}\)
\(\sum_{i=1}^n(s_i-\sum_{j=1}^{i-1}[s_j<s_i])*(n-i+1)!\)
\(f(k)=\sum_{i=0}^ny_i* \prod_{i!=j}\dfrac{k-x_j}{x_i-x_j}\)
来源：博客园
作者：konjac_tbr
链接：https://www.cnblogs.com/bcoier/p/11774663.html