Both mathematics and computer science are arguably "transnational" subjects: the fundamental questions, methods, and points of view are fairly universal around the world, and the specifics of nationality and geography are mostly irrelevant to scholarship and conversation. What this means for study abroad is that one can study mathematics and computer science almost anywhere in the world (which opens up many opportunities) -- but that studying them abroad might not yield the type of fundamentally different, culturally informed perspectives on the subject matter that one would expect in the arts, social sciences, or humanities. The reasons for a math major to study abroad generally fall into (at least) one of two categories:
Both can be excellent reasons.
The mathematics department encourages students to seek out these opportunities, and many past students have had very rewarding experiences doing so: Recent mathematics majors have studied mathematics in programs in the Universities of New South Wales, Adelaide, and Melbourne in Australia; Oxford, University College London, Queen Mary University, and King's College in England; the University of Saint Andrews in Scotland; the National University of Ireland in Galway; and the American Mathematical Society's Math in Moscow Program in Russia. Quite a few successful math majors have also incorporated non-mathematical semesters abroad into their overall programs, including oceanographic field studies in the Turks and Caicos Islands, art courses in Florence, Italy; physics at the European Organization for Nuclear Research (CERN) in Geneva, Switzerland; and international development and Arabic at the American University in Cairo, Egypt.
Our faculty, too, have had diverse international study experiences, and will be more than happy to share them with you.
The mathematics major has a cumulative prerequisite structure, so careful planning is critical. The chairperson of the math department and your advisor will be happy to discuss appropriate course choices with you, and of course, all of us are pleased to engage in informal conversation on the subject.