Find the hidden number "2" by clicking on the tiles to reveal what's behind.

To fill the tile grid, we give each row and column a unique random integer in the range 1–7. We add the numbers and take off one, then find that entry in the list of prime numbers (2,3,5,7,11,...).

For example, a tile with indexes (3,4) hides the 3 + 4 - 1 = 6th prime, i.e. 13.

These might be fun for young mathematicians.