\[ 3 \left (2 x^2+1\right ) y''(x)+x \left (x^2+1\right ) y^{(3)}(x)-12 y(x)=0 \] ✓ Mathematica : cpu = 0.229018 (sec), leaf count = 104
\[\left \{\left \{y(x)\to \frac {1}{3} c_1 \left (2 x^2+1\right )+\frac {1}{3} c_2 x \sqrt {x^2+1}-\frac {c_3 \left (2 x^2+1\right ) \left (3 \left (x^4+x^2\right ) \tanh ^{-1}\left (\sqrt {x^2+1}\right )-\sqrt {x^2+1} \left (3 x^2+1\right )\right )}{6 \sqrt {x^2+1} \left (2 x^3+x\right )}\right \}\right \}\] ✓ Maple : cpu = 0.343 (sec), leaf count = 60
\[ \left \{ y \left ( x \right ) ={\frac {1}{x} \left ( 3\,{\it Artanh} \left ( {\frac {1}{\sqrt {{x}^{2}+1}}} \right ) \sqrt {{x}^{2}+1}{\it \_C2}\,{x}^{2}+\sqrt {{x}^{2}+1}{\it \_C1}\,{x}^{2}+2\,{\it \_C3}\,{x}^{3}-3\,{\it \_C2}\,{x}^{2}+{\it \_C3}\,x-{\it \_C2} \right ) } \right \} \]