\[ a^3 x^3 y(x)+3 a^2 x^2 y'(x)+3 a x y''(x)+y^{(3)}(x)=0 \] ✓ Mathematica : cpu = 0.0194221 (sec), leaf count = 68
\[\left \{\left \{y(x)\to e^{-\frac {a x^2}{2}-\sqrt {3} \sqrt {a} x} \left (c_1 e^{\sqrt {3} \sqrt {a} x}+c_3 e^{2 \sqrt {3} \sqrt {a} x}+c_2\right )\right \}\right \}\]
✓ Maple : cpu = 0.031 (sec), leaf count = 37
\[ \left \{ y \left ( x \right ) ={{\rm e}^{-{\frac {a{x}^{2}}{2}}}} \left ( {\it \_C1}+{\it \_C2}\,{{\rm e}^{\sqrt {3}\sqrt {a}x}}+{\it \_C3}\,{{\rm e}^{-\sqrt {3}\sqrt {a}x}} \right ) \right \} \]