I'm not an expert in this nor a lawyer. My understanding is you can't patent an abstract mathematical algorithm in its own right. What you might be able to patent is the application of an algorithm to solving a specific problem. This is a bit of a moving target as there have been some recent legal decisions with regards to software patents.
With regards to ...
Theorems are excluded from patentability.
35 U.S.C. 101 Inventions patentable.
Whoever invents or discovers any new and useful process, machine, manufacture, or composition of matter, or any new and useful improvement thereof, may obtain a patent therefor, subject to the conditions and requirements of this title.