Find the single even number in the grid by clicking on tiles.

All numbers in the grid are prime.

To fill the grid, Max gives each row and column a unique random number in the range 1–7.

He adds the numbers and takes off one, then finds that entry in the list of prime numbers.

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