\[ a y(x)+x^6 y^{(3)}(x)+6 x^5 y''(x)=0 \] ✓ Mathematica : cpu = 0.448262 (sec), leaf count = 101
\[\left \{\left \{y(x)\to c_1 \left (-e^{\frac {\sqrt [3]{a}}{x}}\right ) \left (\sqrt [3]{a}-2 x\right )+c_2 e^{\frac {(-1)^{2/3} \sqrt [3]{a}}{x}} \left (x-\frac {1}{2} (-1)^{2/3} \sqrt [3]{a}\right )+c_3 e^{-\frac {\sqrt [3]{-1} \sqrt [3]{a}}{x}} \left (\frac {1}{2} \sqrt [3]{-1} \sqrt [3]{a}+x\right )\right \}\right \}\]
✓ Maple : cpu = 0.502 (sec), leaf count = 133
\[ \left \{ y \left ( x \right ) =4\,{\it \_C3}\, \left ( \left ( -i/4+1/4\,\sqrt {3} \right ) \sqrt [3]{-{a}^{4}}+ixa \right ) {{\rm e}^{{\frac {i/2\sqrt [3]{-{a}^{4}} \left ( \sqrt {3}-i \right ) }{ax}}}}-4\,{\it \_C2}\, \left ( \left ( -i/4-1/4\,\sqrt {3} \right ) \sqrt [3]{-{a}^{4}}+ixa \right ) {{\rm e}^{{\frac {-i/2\sqrt [3]{-{a}^{4}} \left ( \sqrt {3}+i \right ) }{ax}}}}+2\,{{\rm e}^{-{\frac {\sqrt [3]{-{a}^{4}}}{ax}}}}{\it \_C1}\, \left ( ax+1/2\,\sqrt [3]{-{a}^{4}} \right ) \right \} \]