\[ y''(x)=-\frac {a x y'(x)}{x^2+1}-\frac {b y(x)}{\left (x^2+1\right )^2} \] ✓ Mathematica : cpu = 0.0278908 (sec), leaf count = 106
\[\left \{\left \{y(x)\to c_1 \left (x^2+1\right )^{\frac {2-a}{4}} P_{\frac {a-2}{2}}^{\frac {1}{2} \sqrt {a^2-4 a+4 b+4}}(i x)+c_2 \left (x^2+1\right )^{\frac {2-a}{4}} Q_{\frac {a-2}{2}}^{\frac {1}{2} \sqrt {a^2-4 a+4 b+4}}(i x)\right \}\right \}\]
✓ Maple : cpu = 0.093 (sec), leaf count = 81
\[ \left \{ y \left ( x \right ) ={\it \_C1}\, \left ( {x}^{2}+1 \right ) ^{{\frac {1}{2}}-{\frac {a}{4}}}{\it LegendreP} \left ( {\frac {a}{2}}-1,{\frac {1}{2}\sqrt {{a}^{2}-4\,a+4\,b+4}},ix \right ) +{\it \_C2}\, \left ( {x}^{2}+1 \right ) ^{{\frac {1}{2}}-{\frac {a}{4}}}{\it LegendreQ} \left ( {\frac {a}{2}}-1,{\frac {1}{2}\sqrt {{a}^{2}-4\,a+4\,b+4}},ix \right ) \right \} \]