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Re:说说啥题?

Posted by swgr at 2008-10-25 21:00:57
In Reply To:说说啥题? Posted by:RoBa at 2008-10-25 20:58:31

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))

Followed by:

C是指组合数么？ (102) RoBa 2008-10-25 21:16:53
- Re:C是指组合数么？ (2) swgr 2008-10-25 21:24:03
  - 目前就只发现了对于素数p, Gcd(p) = p. -_- (6) RoBa 2008-10-25 21:35:53
可能没什么公式，不过可以O（（n*logn）^2）的预处理，O（1）的读取 (102) ever_IMOer 2008-10-25 22:20:23

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