\[ -a y(x)+(b-x) y'(x)+x y''(x)=0 \] ✓ Mathematica : cpu = 0.0126111 (sec), leaf count = 24
DSolve[-(a*y[x]) + (b - x)*Derivative[1][y][x] + x*Derivative[2][y][x] == 0,y[x],x]
\[\{\{y(x)\to c_1 U(a,b,x)+c_2 L_{-a}^{b-1}(x)\}\}\] ✓ Maple : cpu = 0.061 (sec), leaf count = 17
dsolve(x*diff(diff(y(x),x),x)+(b-x)*diff(y(x),x)-a*y(x)=0,y(x))
\[y \left (x \right ) = c_{1} \KummerM \left (a , b , x\right )+c_{2} \KummerU \left (a , b , x\right )\]