This course introduces key mathematical concepts used in computer science, and in particular it prepares students for proof-based CS courses such as CS 21 and CS 38. Mathematical topics are illustrated via applications in Computer Science. CS 1 is a co-requisite as there will be a small number of programming assignments. The course covers basic set theory, induction and inductive structures (e.g., lists and trees), asymptotic analysis, and elementary combinatorics, number theory, and graph theory. Applications include number representation, basic cryptography, basic algorithms on trees, numbers, and polynomials, social network graphs, compression, and simple error-correcting codes.