\[ y''(x)-\left (2 e^x+1\right ) y'(x)+e^{2 x} y(x)-e^{3 x}=0 \] ✓ Mathematica : cpu = 0.0487571 (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 = 0.31 (sec), leaf count = 34
\[\left \{y \left (x \right ) = c_{1} \cosh \left (\frac {x}{2}\right ) {\mathrm e}^{\frac {x}{2}+{\mathrm e}^{x}}+c_{2} {\mathrm e}^{\frac {x}{2}+{\mathrm e}^{x}} \sinh \left (\frac {x}{2}\right )+{\mathrm e}^{x}+2\right \}\]