To play the game, you'll need fifteen game pieces. They can be pennies, match sticks, toothpicks, Cheerios or any other item...so long as you have fifteen of them. Arrange them in three rows; three in one row, five in another and the remaining seven in the last row. Why not call the game 3-5-7?
x x x x x
x x x x x x x
Two players take turns removing items. On each turn a player may take as many or as few (at least one) items from any one row. The player that takes the last item loses. The player that goes first has an advantage; it is his game to win or lose. If he makes no mistakes, he will win. Eventually, you will find that there are certain combinations that are winners if you can leave them for your opponent. It is a fun way to spend a few moments and similar to playing Tic Tac Toe except that there are no draws.
Have fun with it. Take turns going first until one of you figures it out; then let the other person go first every time.
If there are any gamers out there, post your comment by removing some of the x's from any one of the rows. I'll take my turn in response.