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[HEOI2016]求和 | K-D Space #38

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EndSaH opened this issue Jun 4, 2020 · 0 comments
Open

[HEOI2016]求和 | K-D Space #38

EndSaH opened this issue Jun 4, 2020 · 0 comments

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@EndSaH
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EndSaH commented Jun 4, 2020

https://endsah.tk/blog/HEOI2016-%E6%B1%82%E5%92%8C/#more

Description给出 $n$,求$$\sum _{i = 0} ^n \sum _{j = 0} ^i \begin{Bmatrix} i \ j \end{Bmatrix} j! 2 ^j$$其中 $\begin{Bmatrix} i \ j \end{Bmatrix}$ 表示第二类斯特林数,也即将 $i$ 划分成 $j$ 个非空集合的方案数。$$1 \le n \le 10 ^5 \

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