\[ y''(x)-\left (2 e^x+1\right ) y'(x)+e^{2 x} y(x)-e^{3 x}=0 \] ✓ Mathematica : cpu = 0.0429803 (sec), leaf count = 28
\[\left \{\left \{y(x)\to e^x+c_1 e^{e^x}+c_2 e^{x+e^x}+2\right \}\right \}\] ✓ Maple : cpu = 0.291 (sec), leaf count = 34
\[y \relax (x ) = {\mathrm e}^{{\mathrm e}^{x}+\frac {x}{2}} \sinh \left (\frac {x}{2}\right ) c_{2}+{\mathrm e}^{{\mathrm e}^{x}+\frac {x}{2}} \cosh \left (\frac {x}{2}\right ) c_{1}+{\mathrm e}^{x}+2\]