The Hermite-Joubert problem and a conjecture of Brassil-Reichstein

We show that Hermite theorem fails for every integer $n$ of the form $3^{k_1}+3^{k_2}+3^{k_3}$ with integers $k_1>k_2>k_3\ge 0$. This confirms a conjecture of Brassil and Reichstein. We also obtain new results for the relative Hermite-Joubert problem over a finitely generated field of characteristic $0$.