<p>Maybe you know this already, but if not it’s important to know that university-level math is VERY different from the stuff you learn in high school. It’s infinitely more interesting (well, in my opinion), but if you’re not prepared the transition might be jarring. It’s also not unheard of for people who think they like math to find out that they really don’t, once they encounter the “real thing”. Do you have any experience with writing proofs? </p>
<p>The standard “core” math courses are Real/Complex Analysis, Abstract Algebra, theoretical Linear Algebra (sometimes lumped in with abstract algebra), and Topology. There are also plenty of cool electives you might take, such as number theory, combinatorics, logic, etc. </p>
<p>Doing a CS minor or at least learning how to program is really good idea, since a lot of jobs that hire math majors involve computers in some way (certainly not all of them, though). In addition, theoretical computer science is basically a branch of math, but if you only do a minor you might not take those types of classes.</p>