\[ y^{(3)}(x) \left (y'(x)^2+1\right )-3 y'(x) y''(x)^2=0 \] ✓ Mathematica : cpu = 0.132276 (sec), leaf count = 95
\[\left \{\left \{y(x)\to c_3-\frac {i \sqrt {c_1^2 x^2+2 c_2 c_1^2 x+c_2^2 c_1^2-1}}{c_1}\right \},\left \{y(x)\to c_3+\frac {i \sqrt {c_1^2 x^2+2 c_2 c_1^2 x+c_2^2 c_1^2-1}}{c_1}\right \}\right \}\] ✓ Maple : cpu = 0.638 (sec), leaf count = 49
\[ \left \{ y \left ( x \right ) =-\sqrt {-{{\it \_C2}}^{2}-2\,{\it \_C2}\,x-{x}^{2}+{\it \_C1}}+{\it \_C3},y \left ( x \right ) =\sqrt {-{{\it \_C2}}^{2}-2\,{\it \_C2}\,x-{x}^{2}+{\it \_C1}}+{\it \_C3} \right \} \]