\[\frac{6^{n + 1} + 6^{n + 3}}{37} = \frac{6^{n} \cdot 6 + 6^{n} \cdot 6^{3}}{37} =\]
\[= \frac{6 \cdot 6^{n} \cdot \left( 1 + 6^{2} \right)}{37} = 6^{n + 1}\]