The board holds every product of two numbers from 1 to 9, in order. There are exactly 36. Pick how they're laid out: rows, zigzag, or a spiral in or out.
The first player claims any square by naming its factors, like 2 × 9 = 18.
The next player must start with the last number named (9) and picks a second number from the 1 to 9 buttons under the board, like 9 × 4 = 36. Numbers that would land on a taken square are grayed out.
Then the first player starts with that second number (4), and so on.
Win with four of your squares in a row, across, down or diagonal, or when the other player has no move left.