I'm not sure which section you're talking about. If you are in the 4th realm where you obtain the purple key there is a 5 character combination written on the wall a few screens to the left of the combination buttons. Just enter the symbols in the order they are shown. I don't think you are referring to the actual final area, but if you are...
There is a room with 7 combination buttons. You have to solve it from the clues in that room.
The number sequence you gave for the Yeti cave is incorrect. I'm just pointing it out so nobody mistakenly goes by it (like I just did.)