\[\boxed{\mathbf{17.}}\]
\[7 \cdot 2 - 7 = 14 - 7 = 7\]
\[7 \cdot 3 - 7 = 21 - 7 = 14\]
\[7 \cdot 4 - 7 = 28 - 7 = 21\]
\[7 \cdot 5 - 7 = 35 - 7 = 28\]
\[7 \cdot 6 - 7 = 42 - 7 = 35\]
\[7 \cdot 7 - 7 = 49 - 7 = 42\]
\[7 \cdot 8 - 7 = 56 - 7 = 49\]
\[7 \cdot 9 - 7 = 63 - 7 = 56\]