Kind of a "meh" game.
"Test your memory and math skills"
I would argue that a game like Sudoku does a lot more to test memory, as you have to remember more than 3 things to work out the values of the 81 cells, and is a lot more fun and satisfying to complete.
A dozen "rounds" before I increase the difficulty?
Sorry, the game wasn't interesting enough for me to play that long.

Did I get them all correct? Yes
Very easy to memorize 3 number cards for anyone who has ever had to remember a phone number. (3 number groups if you include area code)

The math was also not particularly challenging.

There was no "point" to the game, and not really anything fun about it.

But the game worked, and did what it set out to do.
Rules were clear, and the interface easy to use without mistakes.

Well made. I appreciate the minimalism, that it doesn't have any decoration.
But shouldn't higher levels be worth more points (for unlocking)? imo, the calculations are kind of simple, not very challenging. If there was an option to adjust that, I would probably play this.

nice game