\[ y'(x) (x (a+b)+m+n)+y(x) (a b x+a n+b m)+x y''(x)=0 \] ✓ Mathematica : cpu = 0.0556294 (sec), leaf count = 51
DSolve[(b*m + a*n + a*b*x)*y[x] + (m + n + (a + b)*x)*Derivative[1][y][x] + x*Derivative[2][y][x] == 0,y[x],x]
\[\left \{\left \{y(x)\to c_1 e^{-a x} U(m,m+n,(a-b) x)+c_2 e^{-a x} L_{-m}^{m+n-1}((a-b) x)\right \}\right \}\] ✓ Maple : cpu = 0.09 (sec), leaf count = 39
dsolve(x*diff(diff(y(x),x),x)+((a+b)*x+m+n)*diff(y(x),x)+(a*b*x+a*n+b*m)*y(x)=0,y(x))
\[y \left (x \right ) = {\mathrm e}^{-a x} \left (\KummerM \left (m , m +n , x \left (a -b \right )\right ) c_{1}+\KummerU \left (m , m +n , x \left (a -b \right )\right ) c_{2}\right )\]