Well, I HATE this software argument about patents as, to be honest, EVERYTHING can be described as mathematics.
It's really just an argument used by lazy thinkers. They don't want software patents (with good reasons, because there is a huge number of software patents that are in my opinion obvious), they read that maths is not patentable, so they shout "software is maths, so it is not patentable". There are a few huge problems with it:
1. You can of course claim that all software is maths, and call everyone stupid who doesn't believe it, but that doesn't make it true. If someone says "it is a mathematical function", I say "show me the function". Which never happens.
2. Mathematical formulas cannot be patented because that would forever (or several years) completely block the use of that function for anything. However, even if a program is a mathematical function, the slightest change to that program creates a very much different mathematical function.
3. Here's the big one, probably a bit hard to understand: When laws are created, the law makers want to achieve some effect, and pick the words for the law that seem best to achieve that effect. If you then find out that the words don't actually mean what the lawmakers thought they mean, the result is not that the effect of the law changes, but that the wording of the law changes. For example, if people made laws concerning vegetables and wanted tomatoes included but didn't realise that tomatoes are a fruit and not a vegetable, that would just mean that the wording of the law is going to change. If you convince lawmakers that software isn't patentable because it is maths, but the lawmakers want software to be patentable, they will just change the wording of the law. So nothing would be achieved.