$\displaystyle{ A_n = 4^{3^n}+2^{3^n}+1 }$
In the notation of John Cosgrave, the Saouter numbers are generated by the sequence $\displaystyle{ F_{n,2} }$. Due to this, these numbers share similar properties to those held by Fermat numbers. These numbers were named by Tony Reix[1][2] after Yannick Saouter, who studied these numbers[3].