I’d like to ask the good people of this community that, if you do know the solution or figure it out, that you not share the answer here. Feel free to announce your success, but there’s something to be said for discovering the answer completely unaided, even if it takes years.
It’s embarrassingly obvious once you see it though.
There is one obvious rule that almost works but doesn’t fit one number. This distraction draws your attention, making you more likely to miss the actual rule. It’s a kind of misdirection.