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可能没什么公式，不过可以O（（n*logn）^2）的预处理，O（1）的读取

Posted by ever_IMOer at 2008-10-25 22:20:23 and last updated at 2008-10-25 22:41:13
In Reply To:Re:说说啥题? Posted by:swgr at 2008-10-25 21:00:57 
> 给出n，求F(n)。
> 
> F(n) = sigma(i = 3 to n) Gcd(i);
> 
> Gcd(x) = gcd(C(1,x),C(2,x),...,C(x-1,x))
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