Worlfram Alpha
Wolfram Alpha is capable of solving all sorts of problems and does it quite well. This is a useful and premium app, so you have to pay for it. The app has a wide range of math functions, including number theory, statistics, algebra, and others. The app also includes explaining and responding to requests for help if you need it. This is a legacy application, but it offers products if you are looking for a broad math application that can solve other problems.