\[\boxed{\mathbf{280}.}\]
\[(8n + 3)\ \vdots m;\ \ (7n + 1) \vdots m;\ \ \]
\[m \neq 1:\]
\[\left\{ \begin{matrix} 7 \cdot (8n + 3) \vdots m \\ 8 \cdot (7n + 1) \vdots m \\ \end{matrix} \right.\ \text{\ \ \ \ \ \ \ }\]
\[\ \left\{ \begin{matrix} 56n + 21 \vdots m \\ 56n + 8 \vdots m\ \ \\ \end{matrix} \right.\ ( - )\]
\[13\ \vdots m.\]
\[Ответ:m = 13.\]