160 Brain-Straining Number Placing Games

Sudoku is a number placement puzzle, the aim of which is to enter a number from 1 through 9 in each cell of a grid, most frequently a 9x9 grid made up of 3x3 subgrids (called "regions"), starting with randomly placed numbers given in some cells (the "givens"). Each row, column and region must contain only one instance of each number.