✓ Mathematica : cpu = 0.0088944 (sec), leaf count = 24
DSolve[6*Derivative[1][y][x] + 6*x*Derivative[2][y][x] + x^2*Derivative[3][y][x] == 0,y[x],x]
✓ Maple : cpu = 0.011 (sec), leaf count = 16
dsolve(x^2*diff(diff(diff(y(x),x),x),x)+6*x*diff(diff(y(x),x),x)+6*diff(y(x),x)=0,y(x))