\[ \boxed { {\frac {{\rm d}^{2}}{{\rm d}{x}^{2}}}y \left ( x \right ) +{{\rm e}^{x}}\sin \left ( y \left ( x \right ) \right ) =0} \]
Mathematica: cpu = 1.086138 (sec), leaf count = 18 \[ \text {DSolve}\left [y''(x)+e^x \sin (y(x))=0,y(x),x\right ] \]
Maple: cpu = 0.733 (sec), leaf count = 0 \[ \text {could not solve} \]