For example if I wanted to write $x$ as the sum of $n$ squares in $m$ different ways, is there something I can just look up? Also I have other constraints with what I am working with, if I knew $x$ I could just type the equation into Wolfram Alpha, but what if I wanted to write for example the smallest number which can be written as the sum of n squares in m different ways.
Also are there solutions to $a^{2}+b^{2}=c^{2}+d^{2}$, where $a+b=c+d$ and $a, b, c, d \neq 0$.
Note: I am looking for rational solutions.