\[ y(x)^3 y''(x)-a=0 \] ✓ Mathematica : cpu = 2.1481 (sec), leaf count = 88
\[\left \{\left \{y(x)\to -\frac {\sqrt {a+c_1{}^2 x^2+2 c_2 c_1{}^2 x+c_2{}^2 c_1{}^2}}{\sqrt {c_1}}\right \},\left \{y(x)\to \frac {\sqrt {a+c_1{}^2 x^2+2 c_2 c_1{}^2 x+c_2{}^2 c_1{}^2}}{\sqrt {c_1}}\right \}\right \}\] ✓ Maple : cpu = 1.566 (sec), leaf count = 46
\[\left \{y \left (x \right ) = \frac {\sqrt {c_{1} \left (\left (c_{2}+x \right )^{2} c_{1}^{2}+a \right )}}{c_{1}}, y \left (x \right ) = -\frac {\sqrt {c_{1} \left (\left (c_{2}+x \right )^{2} c_{1}^{2}+a \right )}}{c_{1}}\right \}\]