Linear growth for semigroups which are disjoint unions of finitely many copies of the free monogenic semigroup
Nabilah Hani Abughazalah, Pavel I. Etingof · arXiv (Cornell University) · 2015
We show that every semigroup which is a finite disjoint union of copies of the free monogenic semigroup (natural numbers under addition) has linear growth. This implies that the the corresponding semigroup algebra is a PI algebra.