I do have a table of data.
Lets say 20 rows by 20 columns as a sheet of data on X- and Y-values
Now, I try to find a formula which describes the function for Z, using the table of X,Y-values.
Is there a way in Wolfram Alpha to search for the formula?
Searching for a forumla is a vague task where a lot is left up to interpretation.
Normally you have to do some work in choosing which kinds of functions you want to be the basis that you interpolate the data with.
In this case, you may want to create an interpolation, but this would need to be done with Mathematica since some programming needs to be done.
I remember hearing a talk on evolving functions to fit data at one of the Wolfram conferences.
Does your 20 x 20 table contain x,y values or z values?
I suspect you mean that it contains z values and the x and y values are implicit in the table indices.