\[ y''(x)=\frac {y(x)}{e^x+1} \] ✓ Mathematica : cpu = 0.285257 (sec), leaf count = 42
DSolve[Derivative[2][y][x] == y[x]/(1 + E^x),y[x],x]
\[\left \{\left \{y(x)\to c_1 \left (e^{-x}+1\right )+c_2 e^{-x} \left (e^x \log \left (e^x+1\right )+\log \left (e^x+1\right )+1\right )\right \}\right \}\] ✓ Maple : cpu = 0.024 (sec), leaf count = 27
dsolve(diff(diff(y(x),x),x) = 1/(exp(x)+1)*y(x),y(x))
\[y \left (x \right ) = \left (c_{1} \left ({\mathrm e}^{x}+1\right ) \ln \left ({\mathrm e}^{x}+1\right )+c_{2} {\mathrm e}^{x}+c_{1}+c_{2}\right ) {\mathrm e}^{-x}\]