If the game freezes, just click inside it (games can get unresponsive if you click elsewhere on the page).
Play the sudoku game. The entire table is divided in 16 sections, each of 4x4 boxes. Assign numbers 0 to 15 (a = 10, b = 11, c = 12, d = 13, e = 14, f = 15) in the empty boxes so that in each section, row and column all numbers from 0 to 15 are present without repetitions.
Click on the numbers in the top right part of the screen to select the number. Click on an empty box to write the number. Click on a previous written number to delete it.
Game is completely controlled by mouse.