This is the fourth in a series of proceedings of the Combinatorial and Additive Number Theory Conferences that have been held every year since 1983 at the CUNY Graduate Center in New York. This volume is based on talks from the 2019 and 2020 Combinatorial and Additive Number Theory (CANT) workshops at the City University of New York, the latter of which was held online due to the COVID-19 pandemic and featured speakers from North and South America, Europe, and Asia, making it the largest CANT conference in terms of number of both lectures and participants.These proceedings contain peer-reviewed and edited papers on current topics in number theory. Held every year since 2003, the workshop series surveys state-of-the-art open problems in combinatorial and additive number theory and related parts of mathematics. Topics featured in this volume include sumsets, partitions, convex polytopes and discrete geometry, Ramsey theory, commutative algebra and discrete geometry, and applications of logic and nonstandard analysis to number theory. Each contribution is dedicated to a specific topic that reflects the latest results by experts in the field. This selection of articles will be of relevance to both researchers and graduate students interested in current progress in number theory. weiterlesen