\[ a^3 (-y(x))+3 a^2 y'(x)-3 a y''(x)-e^{a x}+y^{(3)}(x)=0 \] ✓ Mathematica : cpu = 0.010086 (sec), leaf count = 46
\[\left \{\left \{y(x)\to \frac {1}{6} x^3 e^{a x}+c_3 x^2 e^{a x}+c_2 x e^{a x}+c_1 e^{a x}\right \}\right \}\] ✓ Maple : cpu = 0.026 (sec), leaf count = 27
\[\left \{y \left (x \right ) = \frac {\left (x^{3}+6 c_{3} x^{2}+6 c_{2} x +6 c_{1}\right ) {\mathrm e}^{a x}}{6}\right \}\]