\[ \boxed { {\frac {{\rm d}^{3}}{{\rm d}{x}^{3}}}y \left ( x \right ) +{\it a2}\,{\frac {{\rm d}^{2}}{{\rm d}{x}^{2}}}y \left ( x \right ) +{\it a1}\,{\frac {\rm d}{{\rm d}x}}y \left ( x \right ) +{\it a0}\,y \left ( x \right ) =0} \]
Mathematica: cpu = 0.005001 (sec), leaf count = 84 \[ \left \{\left \{y(x)\to c_1 e^{x \text {Root}\left [\text {$\#$1}^3+\text {$\#$1}^2 \text {a2}+\text {$\#$1} \text {a1}+\text {a0}\& ,1\right ]}+c_2 e^{x \text {Root}\left [\text {$\#$1}^3+\text {$\#$1}^2 \text {a2}+\text {$\#$1} \text {a1}+\text {a0}\& ,2\right ]}+c_3 e^{x \text {Root}\left [\text {$\#$1}^3+\text {$\#$1}^2 \text {a2}+\text {$\#$1} \text {a1}+\text {a0}\& ,3\right ]}\right \}\right \} \]
Maple: cpu = 0.015 (sec), leaf count = 644 \[ \left \{ y \left ( x \right ) ={\it \_C1}\,{{\rm e}^{-{\frac {x}{12} \left ( i \left ( 36\,{\it a1}\,{\it a2}-108\,{\it a0}-8\,{{\it a2}}^{3 }+12\,\sqrt {12\,{\it a0}\,{{\it a2}}^{3}-3\,{{\it a1}}^{2}{{\it a2}}^ {2}-54\,{\it a1}\,{\it a2}\,{\it a0}+12\,{{\it a1}}^{3}+81\,{{\it a0}} ^{2}} \right ) ^{{\frac {2}{3}}}\sqrt {3}-4\,i\sqrt {3}{{\it a2}}^{2}+ 12\,i\sqrt {3}{\it a1}+ \left ( 36\,{\it a1}\,{\it a2}-108\,{\it a0}-8 \,{{\it a2}}^{3}+12\,\sqrt {12\,{\it a0}\,{{\it a2}}^{3}-3\,{{\it a1}} ^{2}{{\it a2}}^{2}-54\,{\it a1}\,{\it a2}\,{\it a0}+12\,{{\it a1}}^{3} +81\,{{\it a0}}^{2}} \right ) ^{{\frac {2}{3}}}+4\,{\it a2}\,\sqrt [3]{ 36\,{\it a1}\,{\it a2}-108\,{\it a0}-8\,{{\it a2}}^{3}+12\,\sqrt {12\, {\it a0}\,{{\it a2}}^{3}-3\,{{\it a1}}^{2}{{\it a2}}^{2}-54\,{\it a1} \,{\it a2}\,{\it a0}+12\,{{\it a1}}^{3}+81\,{{\it a0}}^{2}}}+4\,{{\it a2}}^{2}-12\,{\it a1} \right ) {\frac {1}{\sqrt [3]{36\,{\it a1}\,{\it a2}-108\,{\it a0}-8\,{{\it a2}}^{3}+12\,\sqrt {12\,{\it a0}\,{{\it a2} }^{3}-3\,{{\it a1}}^{2}{{\it a2}}^{2}-54\,{\it a1}\,{\it a2}\,{\it a0} +12\,{{\it a1}}^{3}+81\,{{\it a0}}^{2}}}}}}}}+{\it \_C2}\,{{\rm e}^{{ \frac {x}{12} \left ( i \left ( 36\,{\it a1}\,{\it a2}-108\,{\it a0}-8\, {{\it a2}}^{3}+12\,\sqrt {12\,{\it a0}\,{{\it a2}}^{3}-3\,{{\it a1}}^{ 2}{{\it a2}}^{2}-54\,{\it a1}\,{\it a2}\,{\it a0}+12\,{{\it a1}}^{3}+ 81\,{{\it a0}}^{2}} \right ) ^{{\frac {2}{3}}}\sqrt {3}-4\,i\sqrt {3}{{ \it a2}}^{2}+12\,i\sqrt {3}{\it a1}- \left ( 36\,{\it a1}\,{\it a2}-108 \,{\it a0}-8\,{{\it a2}}^{3}+12\,\sqrt {12\,{\it a0}\,{{\it a2}}^{3}-3 \,{{\it a1}}^{2}{{\it a2}}^{2}-54\,{\it a1}\,{\it a2}\,{\it a0}+12\,{{ \it a1}}^{3}+81\,{{\it a0}}^{2}} \right ) ^{{\frac {2}{3}}}-4\,{\it a2} \,\sqrt [3]{36\,{\it a1}\,{\it a2}-108\,{\it a0}-8\,{{\it a2}}^{3}+12 \,\sqrt {12\,{\it a0}\,{{\it a2}}^{3}-3\,{{\it a1}}^{2}{{\it a2}}^{2}- 54\,{\it a1}\,{\it a2}\,{\it a0}+12\,{{\it a1}}^{3}+81\,{{\it a0}}^{2} }}-4\,{{\it a2}}^{2}+12\,{\it a1} \right ) {\frac {1}{\sqrt [3]{36\,{ \it a1}\,{\it a2}-108\,{\it a0}-8\,{{\it a2}}^{3}+12\,\sqrt {12\,{\it a0}\,{{\it a2}}^{3}-3\,{{\it a1}}^{2}{{\it a2}}^{2}-54\,{\it a1}\,{ \it a2}\,{\it a0}+12\,{{\it a1}}^{3}+81\,{{\it a0}}^{2}}}}}}}}+{\it \_C3}\,{{\rm e}^{{\frac {x}{6} \left ( \left ( 36\,{\it a1}\,{\it a2}- 108\,{\it a0}-8\,{{\it a2}}^{3}+12\,\sqrt {12\,{\it a0}\,{{\it a2}}^{3 }-3\,{{\it a1}}^{2}{{\it a2}}^{2}-54\,{\it a1}\,{\it a2}\,{\it a0}+12 \,{{\it a1}}^{3}+81\,{{\it a0}}^{2}} \right ) ^{{\frac {2}{3}}}-2\,{ \it a2}\,\sqrt [3]{36\,{\it a1}\,{\it a2}-108\,{\it a0}-8\,{{\it a2}}^ {3}+12\,\sqrt {12\,{\it a0}\,{{\it a2}}^{3}-3\,{{\it a1}}^{2}{{\it a2} }^{2}-54\,{\it a1}\,{\it a2}\,{\it a0}+12\,{{\it a1}}^{3}+81\,{{\it a0 }}^{2}}}+4\,{{\it a2}}^{2}-12\,{\it a1} \right ) {\frac {1}{\sqrt [3]{ 36\,{\it a1}\,{\it a2}-108\,{\it a0}-8\,{{\it a2}}^{3}+12\,\sqrt {12\, {\it a0}\,{{\it a2}}^{3}-3\,{{\it a1}}^{2}{{\it a2}}^{2}-54\,{\it a1} \,{\it a2}\,{\it a0}+12\,{{\it a1}}^{3}+81\,{{\it a0}}^{2}}}}}}}} \right \} \]