Example. Divide 20 people into 4 groups, with each group having $4,5,5,6$ people, how many ways are there to do this?
Given $m=20, t=3, h_{1}=1, h_{2}=2, h_{3}=1$, hence
$$
\begin{aligned}
f_{20}^{4}= & \frac{20!}{4!\cdot 5!\cdot 5!\cdot 6!\cdot 1!\cdot 2!\cdot 1!} \\
& =4888643760 .
\end{aligned}
$$