\[ \boxed { 2\, \left ( {\frac {\rm d}{{\rm d}x}}y \left ( x \right ) \right ) {\frac {{\rm d}^{3}}{{\rm d}{x}^{3}}}y \left ( x \right ) -3\, \left ( {\frac {\rm d}{{\rm d}x}}y \left ( x \right ) \right ) ^{2}=0} \]
Mathematica: cpu = 0.040505 (sec), leaf count = 51 \[ \left \{\left \{y(x)\to c_1\right \},\left \{y(x)\to \sqrt {\frac {2}{3}} e^{-\sqrt {\frac {3}{2}} x} \left (c_1 e^{\sqrt {6} x}-c_2\right )+c_3\right \}\right \} \]
Maple: cpu = 0.0 (sec), leaf count = 28 \[ \left \{ y \left ( x \right ) ={\it \_C1},y \left ( x \right ) ={\it \_C1} +{\it \_C2}\,{{\rm e}^{{\frac {\sqrt {6}x}{2}}}}+{\it \_C3}\,{{\rm e}^ {-{\frac {\sqrt {6}x}{2}}}} \right \} \]