\[ -a x y'(x)+x^3+y'(x)^3=0 \] ✗ Mathematica : cpu = 299.998 (sec), leaf count = 0 , timed out
$Aborted
✓ Maple : cpu = 0.057 (sec), leaf count = 231
\[ \left \{ y \left ( x \right ) =\int \!{i \left ( \left ( {\frac {i}{12}}-{\frac {\sqrt {3}}{12}} \right ) \left ( -108\,{x}^{3}+12\,\sqrt {-12\,{a}^{3}{x}^{3}+81\,{x}^{6}} \right ) ^{{\frac {2}{3}}}+ \left ( \sqrt {3}+i \right ) xa \right ) {\frac {1}{\sqrt [3]{-108\,{x}^{3}+12\,\sqrt {-12\,{a}^{3}{x}^{3}+81\,{x}^{6}}}}}}\,{\rm d}x+{\it \_C1},y \left ( x \right ) =\int \!{i \left ( \left ( {\frac {i}{12}}+{\frac {\sqrt {3}}{12}} \right ) \left ( -108\,{x}^{3}+12\,\sqrt {-12\,{a}^{3}{x}^{3}+81\,{x}^{6}} \right ) ^{{\frac {2}{3}}}+x \left ( i-\sqrt {3} \right ) a \right ) {\frac {1}{\sqrt [3]{-108\,{x}^{3}+12\,\sqrt {-12\,{a}^{3}{x}^{3}+81\,{x}^{6}}}}}}\,{\rm d}x+{\it \_C1},y \left ( x \right ) =\int \!{\frac {1}{6} \left ( \left ( -108\,{x}^{3}+12\,\sqrt {-12\,{a}^{3}{x}^{3}+81\,{x}^{6}} \right ) ^{{\frac {2}{3}}}+12\,ax \right ) {\frac {1}{\sqrt [3]{-108\,{x}^{3}+12\,\sqrt {-12\,{a}^{3}{x}^{3}+81\,{x}^{6}}}}}}\,{\rm d}x+{\it \_C1} \right \} \]