They started numbering the episodes differently starting in Season 43. Prior to that, they counted each individual episode. From Season 43 onward, the season 43 premiere was 4301, the season 44 premiere was 4401, and it would go on like that. The first 2 digits of the episode number is the season number, and the last 2 digits is which episode it is of the season. So episode 4610 = the 10th episode of season 46. Much better way to keep track of episodes.