It is true that an algorithm can be converted to a formula, and a formula to an algorithm, but it is unlikely a given useful algorithm could be generated mechanically from a (human-written, useful) formula.

For example, you could write a formula to express the property of order in lists, and maybe with some mechanical procedure (falling under "obvious to the person skilled in the art") you could then generate an algorithm that sorted lists. However, what's the time/space complexity of that algorithm? What are the practical runtime characteristics? For industry applications the practical runtime characteristics matter as much as anything else. That you technically could compute something doesn't matter at all, if that computation might not finish until relevant celestial bodies have phase changes.

I'm not saying Quicksort should be patentable, but I do think it's at least a step and a half removed from pure math.