DSolve[-A[1] - x*(-A[0] + a*A[1]) - (A[2] + x*(-A[1] + a*A[2]))*Derivative[1][y][x] - (A[3] + x*(-A[2] + a*A[3]))*Derivative[2][y][x] - (A[4] + x*(-A[3] + a*A[4]))*Derivative[3][y][x] - (A[5] + x*(-A[4] + a*A[5]))*Derivative[4][y][x] + x*Derivative[5][y][x] == 0,y[x],x]