Calcudoku

Calcudoku puzzle (also known as Mathdoku, Newdoku, or KenKen) is similar to Sudoku, but requires basic math skills to solve.   The goal of each puzzle is to fill a grid with digits; 1 through 4 for a 4x4 grid, 1 through 5 for a 5x5, and so on.   Each digit can appear only once in each row and in each column.