\[ \boxed { {x}^{2}{\it d4y} \left ( x \right ) +2\,x{\frac {{\rm d}^{3}}{{\rm d}{x}^{3}}}y \left ( x \right ) +ay \left ( x \right ) -b{x}^{2}=0} \]
Mathematica: cpu = 0 (sec), leaf count = 0 \[ \text {Hanged} \]
Maple: cpu = 0.047 (sec), leaf count = 89 \[ \left \{ y \left ( x \right ) ={\frac {b{x}^{2}}{a}}+{\it \_C1}\,\sqrt { x}{{\sl J}_{1}\left (2\,\sqrt [4]{-a}\sqrt {x}\right )}+{\it \_C2}\, \sqrt {x}{{\sl Y}_{1}\left (2\,\sqrt [4]{-a}\sqrt {x}\right )}+{\it \_C3 }\,\sqrt {x}{{\sl J}_{1}\left (2\,\sqrt {-\sqrt {-a}}\sqrt {x}\right )}+ {\it \_C4}\,\sqrt {x}{{\sl Y}_{1}\left (2\,\sqrt {-\sqrt {-a}}\sqrt {x} \right )} \right \} \]