\[ y''(x)=\frac {y(x)}{e^x+1} \] ✓ Mathematica : cpu = 0.336037 (sec), leaf count = 42
\[\left \{\left \{y(x)\to c_1 \left (e^{-x}+1\right )+c_2 e^{-x} \left (e^x \log \left (e^x+1\right )+\log \left (e^x+1\right )+1\right )\right \}\right \}\]
✓ Maple : cpu = 0.048 (sec), leaf count = 27
\[ \left \{ y \left ( x \right ) = \left ( \left ( \left ( {{\rm e}^{x}}+1 \right ) ^{-1}+\ln \left ( {{\rm e}^{x}}+1 \right ) \right ) {\it \_C1}+{\it \_C2} \right ) \left ( 1+ \left ( {{\rm e}^{x}} \right ) ^{-1} \right ) \right \} \]