\[ \boxed { \left ( {x}^{2}+1 \right ) {\frac {{\rm d}^{2}}{{\rm d}{x}^{2}}}y \left ( x \right ) +x{\frac {\rm d}{{\rm d}x}}y \left ( x \right ) -9\,y \left ( x \right ) =0} \]
Mathematica: cpu = 0.019502 (sec), leaf count = 25 \[ \left \{\left \{y(x)\to c_1 \cosh \left (3 \sinh ^{-1}(x)\right )+i c_2 \sinh \left (3 \sinh ^{-1}(x)\right )\right \}\right \} \]
Maple: cpu = 0.016 (sec), leaf count = 39 \[ \left \{ y \left ( x \right ) ={\it \_C1}\,\sin \left ( 3\,\arctan \left ( {\frac {x}{\sqrt {-{x}^{2}-1}}} \right ) \right ) +{\it \_C2}\, \cos \left ( 3\,\arctan \left ( {\frac {x}{\sqrt {-{x}^{2}-1}}} \right ) \right ) \right \} \]