[其他] closed formula

[supyou5566 (❺❺❻❻)]

各位好，這裡有個問題想請教大家：

Find a closed formula for the expression


 n
Σ  [k/(n^k)]C(n,k)
k=1


想了很久沒解出來，先謝謝了!

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推 G41271      :kC(n,k)= nC(n-1,k-1)