$ = \left| {\begin{array}{*{20}{c}}
{a + {{\left( { - 1} \right)}^{n + 2}}a}&{a + 1}&{a - 1}\\
{ - b + {{\left( { - 1} \right)}^{n + 1}}b}&{b + 1}&{b - 1}\\
{c + {{\left( { - 1} \right)}^n}c}&{c - 1}&{c + 1}
\end{array}} \right|$
$=0$ if $n$ is an obb integer.