摘要：链接 \[f_{0} = 1,f_{1} = 2,f_{n} = \left( n - 1 \right)f_{n - 1} + \sum_{i = 2}^{n - 2}{\left( i - 1 \right)f_{i}f_{n - i}}\left( n \geq 2 \right) \]从 \ 阅读全文