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摘要： 直接推生成函数，即 $$\begin{align}F(z)&=\frac{1}{1-z^2}\cdot(1+z)\cdot(1+z+z^2)\cdot\frac{z}{1-z^2}\cdot\frac{1}{1-z^4}\cdot(1+z+z^2+z^3)\cdot(1+z)\cdot\frac{1 阅读全文