I happened across the following question:
Determine the number of ways of putting $m$ indistinguishable balls into $n$ indistinguishable boxes with the restriction that no box is empty.
The obvious answer is $\Pi(m,n)$, where $\Pi$ denotes the partition of the positive integer $m$ into $n$ parts. This is not "satisfying". Is there a closed form formula for this $\Pi(m,n)$?