A path formula for the sock sorting problem

Suppose that $n$ different pairs of socks are put in a tumble dryer. When the dryer is finished, socks are taken out one by one. If a sock matches one of the socks on the sorting table, both are removed; otherwise, it is put on the table until its partner emerges from the dryer. We note the number of socks on the table after each of the $2n$ socks is taken from the dryer, and we give an explicit formula for the probability that this sequence equals a given sequence of length $2n$.