\[ \boxed { {x}^{2} \left ( {x}^{2}-1 \right ) {\frac {{\rm d}^{2}}{{\rm d}{x}^{2}}}y \left ( x \right ) -2\,{x}^{3}{\frac {\rm d}{{\rm d}x}}y \left ( x \right ) - \left ( \left ( a-n \right ) \left ( a+n+1 \right ) {x}^{2} \left ( {x}^{2}-1 \right ) +2\,a{x}^{2}+n \left ( n+1 \right ) \left ( {x}^{2}-1 \right ) \right ) y \left ( x \right ) =0} \]
Mathematica: cpu = 14.232807 (sec), leaf count = 115 \[ \left \{\left \{y(x)\to \text {DifferentialRoot}\left (\{\unicode {f818},\unicode {f817}\}\unicode {f4a1}\left \{-2 \unicode {f818}'(\unicode {f817}) \unicode {f817}^3+\left (a^2 \unicode {f817}^4-n^2 \unicode {f817}^4+a \unicode {f817}^4-n \unicode {f817}^4-a^2 \unicode {f817}^2+2 n^2 \unicode {f817}^2+a \unicode {f817}^2+2 n \unicode {f817}^2-n^2-n\right ) \unicode {f818}(\unicode {f817})+\left (\unicode {f817}^4-\unicode {f817}^2\right ) \unicode {f818}''(\unicode {f817})=0,\unicode {f818}(2)=c_1,\unicode {f818}'(2)=c_2\right \}\right )(x)\right \}\right \} \]
Maple: cpu = 0.172 (sec), leaf count = 109 \[ \left \{ y \left ( x \right ) ={\it \_C1}\,{\it HeunC} \left ( 0,-n-{ \frac {1}{2}},-2,-{\frac {{a}^{2}}{4}}+{\frac {{n}^{2}}{4}}-{\frac {a }{4}}+{\frac {n}{4}},-{\frac {{n}^{2}}{4}}-{\frac {n}{4}}+{\frac {3}{4 }}+{\frac {{a}^{2}}{4}}-{\frac {a}{4}},{x}^{2} \right ) {x}^{-n}+{\it \_C2}\,{\it HeunC} \left ( 0,n+{\frac {1}{2}},-2,-{\frac {{a}^{2}}{4}}+ {\frac {{n}^{2}}{4}}-{\frac {a}{4}}+{\frac {n}{4}},-{\frac {{n}^{2}}{4 }}-{\frac {n}{4}}+{\frac {3}{4}}+{\frac {{a}^{2}}{4}}-{\frac {a}{4}},{ x}^{2} \right ) {x}^{n+1} \right \} \]