What exactly are you passing in to the stored procedure? If you could give an example of how this is used it would help. If it truely is 1, 2, 3, 4... 20 then I have no clue why you're passing them in

? I don't think 11.9.2 supports dynamic SQL so you can't perform a loop and insert them with EXEC( .. ). Unfortunately, I think you are going to have to write 20 insert statements. Maybe if you passed them as a single variable (maybe comma delimited?) you could break up the var based upon the comma and insert that in a while loop of some sort?
Or another solution, perform the insert from the client side (e.g. have the stored procedure take one parameter and have the client call it 20 times).