\[ a^3 (-y(x))+3 a^2 y'(x)-3 a y''(x)-e^{a x}+y^{(3)}(x)=0 \] ✓ Mathematica : cpu = 0.0175128 (sec), leaf count = 34
\[\left \{\left \{y(x)\to \frac {1}{6} e^{a x} \left (6 c_3 x^2+6 c_2 x+6 c_1+x^3\right )\right \}\right \}\]
✓ Maple : cpu = 0.02 (sec), leaf count = 27
\[ \left \{ y \left ( x \right ) ={\frac {{{\rm e}^{ax}} \left ( 6\,{\it \_C3}\,{x}^{2}+{x}^{3}+6\,{\it \_C2}\,x+6\,{\it \_C1} \right ) }{6}} \right \} \]