\[ a^3 x^3 y(x)+3 a^2 x^2 y'(x)+3 a x y''(x)+y^{(3)}(x)=0 \] ✓ Mathematica : cpu = 0.0140404 (sec), leaf count = 72
\[\left \{\left \{y(x)\to c_1 e^{-\frac {a x^2}{2}}+c_2 e^{-\frac {a x^2}{2}-\sqrt {3} \sqrt {a} x}+c_3 e^{\sqrt {3} \sqrt {a} x-\frac {a x^2}{2}}\right \}\right \}\] ✓ Maple : cpu = 0.036 (sec), leaf count = 37
\[\left \{y \left (x \right ) = \left (c_{2} {\mathrm e}^{\sqrt {3}\, \sqrt {a}\, x}+c_{3} {\mathrm e}^{-\sqrt {3}\, \sqrt {a}\, x}+c_{1}\right ) {\mathrm e}^{-\frac {a \,x^{2}}{2}}\right \}\]