\[ \boxed { {\frac {{\rm d}^{2}}{{\rm d}{x}^{2}}}y \left ( x \right ) -6\, \left ( y \left ( x \right ) \right ) ^{2}-x=0} \]
Mathematica: cpu = 0.162021 (sec), leaf count = 20 \[ \text {DSolve}\left [y''(x)-6 y(x)^2-x=0,y(x),x\right ] \]
Maple: cpu = 0.094 (sec), leaf count = 0 \[ \text {could not solve} \]