What are your cost constraints?An example of @ucbalumnus suggestion is the University of Wisconsin. At the graduate level they are a top 20 school in math. They are not as difficult in admissions compared to the other to 20 schools. Normally I don’t like using graduate rankings for undergraduates. However, someone that comes in at an advanced standing in a subject is more likely to be taking graduate level classes. The issue is that you will unlikely get any financial aid and the cost will be $55,000+ per year.