The dictionary says Art can refer to 'skill in conducting any human activity', and it also has an archaic usage 'science, learning, or scholarship'. So can we call Mathematics a kind of art or is it appropriate to call it a kind of art nowadays?
A search for "mathematics art or science" finds this interesting article:
My view is that mathematics is neither an art nor a science. A third path exists, nestled between the two, and intertwined with both. Mathematics is inherently different from other disciplines. While it is wildly creative, it is not art. While it can be used to model natural phenomena, it is not science. There are elements of both art and science in the field, but it isn’t a subset of either.
On the other hand, a search for "the art of mathematics" finds many books, so the question "Can we call mathematics a kind of art" must be answered yes, because many do call it that. It just isn't merely that. A painter can create any kind of imaginary world they want; a mathematician must create proofs that others have to agree with.