\[ \boxed { \left ( {x}^{2}-1 \right ) {\frac {{\rm d}^{2}}{{\rm d}{x}^{2}}}y \left ( x \right ) +x{\frac {\rm d}{{\rm d}x}}y \left ( x \right ) +f \left ( x \right ) y \left ( x \right ) =0} \]
Mathematica: cpu = 0.365046 (sec), leaf count = 28 \[ \text {DSolve}\left [f(x) y(x)+\left (x^2-1\right ) y''(x)+x y'(x)=0,y(x),x\right ] \]
Maple: cpu = 0.0 (sec), leaf count = 41 \[ \left \{ y \left ( x \right ) ={\it DESol} \left ( \left \{ {\frac {f \left ( x \right ) {\it \_Y} \left ( x \right ) }{{x}^{2}-1}}+{\frac {x{ \frac {\rm d}{{\rm d}x}}{\it \_Y} \left ( x \right ) }{{x}^{2}-1}}+{ \frac {{\rm d}^{2}}{{\rm d}{x}^{2}}}{\it \_Y} \left ( x \right ) \right \} , \left \{ {\it \_Y} \left ( x \right ) \right \} \right ) \right \} \]