\[ \boxed { {x}^{2}{\frac {{\rm d}^{2}}{{\rm d}{x}^{2}}}y \left ( x \right ) +x{\frac {\rm d}{{\rm d}x}}y \left ( x \right ) - \left ( x+a \right ) y \left ( x \right ) =0} \]
Mathematica: cpu = 0.047506 (sec), leaf count = 78 \[ \left \{\left \{y(x)\to (-1)^{-\sqrt {a}} c_1 \Gamma \left (1-2 \sqrt {a}\right ) I_{-2 \sqrt {a}}\left (2 \sqrt {x}\right )+(-1)^{\sqrt {a}} c_2 \Gamma \left (2 \sqrt {a}+1\right ) I_{2 \sqrt {a}}\left (2 \sqrt {x}\right )\right \}\right \} \]
Maple: cpu = 0.0 (sec), leaf count = 31 \[ \left \{ y \left ( x \right ) ={\it \_C1}\,{{\sl I}_{2\,\sqrt {a}}\left ( 2\,\sqrt {x}\right )}+{\it \_C2}\,{{\sl K}_{2\,\sqrt {a}}\left (2\, \sqrt {x}\right )} \right \} \]