Edit: The first version of this puzzle was apparently too hard. After a days worth of back and forth, I am consolidating all hints, answer attempts, and comments into a restated puzzle here from the point where we collectively had gotten to. We now have actually arrived at the original version of the puzzle before I posted it, which I changed because I thought it would be too easy. I guess we'll find out...
(If you want to see the previous harder version of the puzzle, look back at the edit history.)
My safe has an 8 digit code. Since I was worried I would forget it, I wrote four other 8 digit codes on a piece of paper and taped it to the door of the safe. The code to my safe is the next number in this sequence:
21600991 10707681 40706771 10019491
Can you help me figure out the 8 digit code to open my safe?
People who live in the largest countries in the world may find this question easier to solve than those who don't.