\[ax = - 26\ \ \]
\[x = - \frac{26}{a};\ \ \ x - натуральное\ \]
\[число\]
\[a = \{ - 1;\ - 2;\ - 13;\ - 26\}.\]
\[Ответ:\ \]
\[a = \{ - 1;\ - 2;\ - 13;\ - 26\}.\ \]