this could be the basis for a very cool math game. right now, it needs greater variety and challenges, but there are lots of ways you could get there:
a limited number of numbers that get depleted as you keep playing - this would discourage people from playing the number 1 too often. in other words, you have to think strategically about the next level
bonus points for using the fewest (or most) number of numbers to get to the total
power ups, like subtraction or multiplication signs.
having to click on numbers that are adjacent to each other
having to use a specific number of numbers (e.g. 4 numbers to make 19)
there's actually limitless potential to make the game super varied. i encourage you to keep working on it!