I am reading the Wikipedia article entitiled Sylow theorems. This short segment of the article reads:
Part of Wilson's theorem states that $(p-1)!$ is congruent to $-1$ (mod $p$) for every prime $p$. One may easily prove this theorem by Sylow's third theorem. Indeed, observe that the number $n_p$ of Sylow's $p$-subgroups in the symmetric group $S_p$ is $(p-2)!$. On the other hand, $n_p ≡ 1$ mod p. Hence, $(p-2)! ≡ 1$ mod $p$. So, $(p-1)! ≡ -1$ mod $p$.
I do not understand why the number of Sylow p-subgroups of $S_p$ is $(p-2)! $
I am taking a course in Group Theory and I have studied everything in Dummit and Foote up to Sylow's theorem. I have also had an introductory course in number theory and am familiar with basic combinatorics.
Edit: to satisfy 6 character requirement.