The equation counter should be set to 0 at the start of all sections and subsections that contain equations.
\setcounter{equation}{0}
You may use any of the three single dollar equivalent environments. Any mathematics contained in such structures will not be reflowed in the transformation to large print. They should not be used for anything that is longer than a few words. Encode each separate mathematical “thought” within it’s own dollars. Each time you exit math mode the line-breaking algorithm has a chance to break the line.
\begin{math}A_{i,j,k}^{2^n}\end{math}, \(A_{i,j,k}^{2^n}\), $A_{i,j,k}^{2^n}$
$A_{i,j,k}^{2^ n}$, $A_{i,j,k}^{2^ n}$, $A_{i,j,k}^{2^ n}$