...

And now, a somewhat related original puzzle...

**(3) You are given a stack of cards numbered 1 to n, and their order is randomized. What is the probability that two consecutively numbered cards (lets say, a and a+1) are found consecutively (a immediately before a+1) somewhere in the stack?**

I can calculate this probability as a series, but I haven't found a polynomial solution yet.

But I suppose, EH is looking for a polynomial solution. Is that so?

Or is the problem to calculate probability for

**two specific cards**? But that would be too simple, not EH-like problem.