🔢 237.
You must utterly and completely reject the supernatural interpretation of the film. Kubrick requires you to be a serious adult.
The photographs around the hotel are residue—"like burnt toast"—that only people who shine notice. There are number games everywhere.
Kubrick renamed the room from 217 in the book to 237 in the film. 217 has no geometric meaning. 237 does: it's the diamond pattern. 2 rows, 3 columns, 7 diamonds. The impossible relation.
Room 237 should be in the middle of the Colorado Lounge spatially. There is no room for it. The tricycle scenes prove the continuous layout of the space—like a magician priming the audience with the illusion of physicality before undoing it with the turn and prestige.
The room cannot exist. That's the point.