Superscript and Subscript
superscript
$a^{ xy }$
a^{ xy }
superscript left
${}^{ xy } a$
{}^{ xy } a
subscript
$a_{ xy }$
a_{ xy }
subscript left
${}_{ xy } a$
{}_{ xy } a
subscript sample
$\begin{eqnarray} a_n^2 + a_{ n + 1 }^2 = a_{ 2n + 1 } \end{eqnarray}$
\begin{eqnarray}
a_n^2 + a_{ n + 1 }^2 = a_{ 2n + 1 }
\end{eqnarray}