Hello, NooblasNooblas. Thank you for checking out the game and giving me feedback. Sorry about the annoying window size issues. In the next update I want to try adding more setting options where you can adjust window size among other things.
And to answer your question, I programmed the game so that boards are randomly generated. However, I also programmed the game so that in adventure mode, the number level you are on will always have that number appear on the board. So a 7 will appear on level 7 and an 8 on level 8. That's probably why it feels like you're seeing so many of them.