\[ y''(x)=-\frac {a y(x)}{x^4} \] ✓ Mathematica : cpu = 0.0801479 (sec), leaf count = 52
\[\left \{\left \{y(x)\to c_1 x e^{\frac {i \sqrt {a}}{x}}-\frac {i c_2 x e^{-\frac {i \sqrt {a}}{x}}}{2 \sqrt {a}}\right \}\right \}\] ✓ Maple : cpu = 0.074 (sec), leaf count = 31
\[ \left \{ y \left ( x \right ) =x \left ( \cosh \left ( {\frac {1}{x}\sqrt {-a}} \right ) {\it \_C2}+\sinh \left ( {\frac {1}{x}\sqrt {-a}} \right ) {\it \_C1} \right ) \right \} \]