Semi-magic dihedral squares

Abstract

Let $\Gamma$ be a group of order $n^2$ and $SMS_{\Gamma}(n)=(a_{i,j})_{n\times n}$ be an $n\times n$ array whose entries are all distinct elements of $\Gamma$. If there exists an element $\mu\in\Gamma$ such that for every row $i$, there exists an ordering of elements such that $$ a_{i,j_1} a_{i,j_2} \dots a_{i,j_{n-1}} a_{i,j_n} = \mu $$ and for every column $j$ there exists an ordering of elements such that $$ a_{i_1,j} a_{i_2,j} \dots a_{i_{m-1},j} a_{i_m,j} = \mu, $$ then $SMS_{\Gamma}(n)$ is called a \emph{$\Gamma$-semi-magic square of side $n$} and $\mu$ is called a \emph{magic constant}. We provide a complete characterization of semi-magic squares of side $n$ whose entries belong to a dihedral group $D_k$. Moreover, we show that in our constructions a single semi-magic square may admit two distinct magic constants, depending on the order in which the products are computed.