Why isn't the winning number based on the last character of the block hash of the last bet placed in the group? The way I understand that you've designed this is extremely open to fixing - your system "randomly" picks a number once all the bets are in? How is that provably fair? What stops you from betting in each group and picking your own number?

If that's not the way it works, you should do a better job of explaining because "The winning number determines the blockchain" isn't proper English.