If you are a materialist, then math is absolutely discovered. It is insane to think that aliens would have a math system where 2+2 is not 4.
Mathematical rules are objectal. They are real, objective, but not material. The same way the meaning of the word remains the same no matter who reads it or the number of rocks is independent of the viewer.
This is the reason why universe can be described in the mathematical languge, because math is discovered from the nature.