The "Tic-Tac-Toe" can be played with a paper and a pencil by two players who alternately draw an X and an O in a grid of size 3 X 3. The player who first align three symbols vertically, horizontally or diagonally wins the game.

If played without fail, this is a type of game that always ends in a draw. However, some flaws have been introduced in the programming of this game, in order to allow the computer to sometimes make mistakes!

Despite its apparent simplicity, the "Tic-Tac-Toe" requires detailed analysis to determine the number of possible final positions that is 138. This number is quite complex to calculate. Since the game ends as soon as one of the players has aligned three symbols and also because we have to take into account the symmetries of the board (rotations and reflections). Although the game already existed hundreds of years ago, it was not until 2002 and with the help of computers that mathematicians were able to calculate the number of different possible moves that is 26830.