(Sum from i = 1 to n ((-1)^(i+1) * (n choose 2i) * (2i)! * (n-1)^(n-2i)) / (2^i * i!)) / (n-1)^n

Uh oh! Wolfram|Alpha doesn't run without JavaScript.

Please enable JavaScript. If you don't know how, you can find instructionshere.Once you've done that, refresh this page to start using Wolfram|Alpha.