\[ y'(x) (x (a+b)+m+n)+y(x) (a b x+a n+b m)+x y''(x)=0 \] ✓ Mathematica : cpu = 0.0946846 (sec), leaf count = 51
\[\left \{\left \{y(x)\to c_1 e^{-a x} U(m,m+n,(a-b) x)+c_2 e^{-a x} L_{-m}^{m+n-1}(x (a-b))\right \}\right \}\]
✓ Maple : cpu = 0.102 (sec), leaf count = 43
\[ \left \{ y \left ( x \right ) ={\it \_C1}\,{{\rm e}^{-ax}}{{\sl M}\left (m,\,n+m,\,x \left ( a-b \right ) \right )}+{\it \_C2}\,{{\rm e}^{-ax}}{{\sl U}\left (m,\,n+m,\,x \left ( a-b \right ) \right )} \right \} \]