Advertising finite commutative semigroups

Every mathematician is familiar with the beautiful structure of finite commutative groups. What is less well known is that finite commutative semigroups also have a neat and well-described structure. We prove this in an efficient fashion. We unravel the structural details of many concrete finite commutative semigroups. Here “concrete” comes in two types. First, we examine the structure of the MULTIPLICATIVE semigroups Z/nZ (more interesting than their bland additive siblings) and show that it depends on the prime factors of $n$ in interesting ways. Second, we thoroughly treat finite commutative semigroups defined by generators and relations. Our aim is to provide a comprehensive introduction to the area, including some novel results and some enticing directions for the expert to follow.