A patent is a technical scheme to improve a product or method.

Mathematical theorem is not a technical scheme, so it does not belong to the scope of patent protection.

in addition

Article 25 of the patent law stipulates that

No patent right shall be granted for the following items:

(1) scientific discoveries;

(2) rules and methods of intellectual activities;

(3) Methods of diagnosis and treatment of diseases;

(4) Species of animals and plants;

(5) substances obtained by nuclear transformation;

(six) the design of the pattern, color or the combination of the two.

The production method of the products listed in Item (4) of the preceding paragraph may be granted a patent right in accordance with the provisions of this Law.

Obviously, the mathematical theorem belongs to the second item, and the rules and methods of intellectual activities cannot be patented.