I'm struggling to get the following recurrence relation into a closed form if possible:
$$f(m,0)=f(0,n)=2$$ $$f(0,0)=0$$ $$f(m,n)=f(m-1,n)\cdot(2n+1)(2n+2) + f(m,n-1)\cdot(2m+1)(2m+2)$$
where $m$ and $n$ are non-negative integers. This recurrence relation came from one combinatorics problem and I 'd like to ask how to derive the explicit formula for $f(m,n)$.