Sets avoiding six-term arithmetic progressions in ${\mathbb{Z}}_6^n$ are exponentially small

Abstract

We show that sets avoiding 6-term arithmetic progressions in ${\mathbb{Z}}_6^n$ have size at most $5.709^n$. It is also pointed out that the "product construction" does not work in this setting, specially, we show that for the extremal sizes in small dimensions we have $r_6({\mathbb{Z}}_6)=5$, $r_6({\mathbb{Z}}_6^2)=25$ and $116\le r_6({\mathbb{Z}}_6^3)\le 124$.