what does num_days=int((end_dt-start_dt)/np.timetable64(1,'D')) mean? why does the function np.timetable has a 64 at the end of it?

Question

what does the command code num_days=int((end_dt-start_dt)/np.timetable64(1,\'D\')) mean? why does the function np.timetable has a 64 at the end of it?