\[ -\left (2 e^x+1\right ) y'(x)+y''(x)+e^{2 x} y(x)-e^{3 x}=0 \] ✓ Mathematica : cpu = 0.0510891 (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 = 0.26 (sec), leaf count = 34
\[ \left \{ y \left ( x \right ) ={{\rm e}^{{\frac {x}{2}}+{{\rm e}^{x}}}}\sinh \left ( {\frac {x}{2}} \right ) {\it \_C2}+{{\rm e}^{{\frac {x}{2}}+{{\rm e}^{x}}}}\cosh \left ( {\frac {x}{2}} \right ) {\it \_C1}+{{\rm e}^{x}}+2 \right \} \]