Obviously the least Hook number is 1, by considering boxes stacked vertically or horizontally. Is there a formula for the greatest possible Hook number ?
EDIT: The Hook number of a Young diagram is defined to be the number of standard Young tableaux whose shape is that of the Young diagram.
Too long for a comment, but I wrote some Python code to compute the partition(s) of $n$ which attain the maximal hook number. It is brute force, so it is only feasible for sufficiently small $n$, say $n\le 50$. Link to code.
Here are the optimal partitions for $n$ between $28$ and $36$. There seems to always be exactly one or two partitions attaining the maximum. The optimal partitions are also roughly triangular, even though the triangular partition $(m,m-1,\dots,2,1)$ is itself not optimal except for small enough $m$.