Any system with known, fully-specified constraints is "math". That's the only definition of "math" that actually covers all the things mathematicians do. Algebra/calculus, set/group theory, logic (various forms), graph theory, and such are all undisputed branches of "mathematics". I defy anyone to come up with a definition of "mathematics" that includes things like the above, but does not include computing. (And no cheating: simply listing existing branches of mathematics is not persuasive.)
That said, this argument is a bit of a non-starter: software is mathematics, sure, but mathematics are not patentable by legislation (at least in the U.S.). Legislation is easy to change, and it likely will be when people finally accept the "mathematics = software" argument.