\[ y''(x)=\frac {y(x)}{e^x+1} \] ✓ Mathematica : cpu = 0.312218 (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 = 0.023 (sec), leaf count = 27
\[\{y \left (x \right ) = \left (c_{1} \left ({\mathrm e}^{x}+1\right ) \ln \left ({\mathrm e}^{x}+1\right )+c_{2} {\mathrm e}^{x}+c_{1}+c_{2}\right ) {\mathrm e}^{-x}\}\]