Tri-doku  (English, Paperback, Light Japheth J.)

Its the new shape of sudoku! These fun and extra-challenging puzzles come in triangles, all colour-coded to indicate special spaces where numbers can't repeat and where new rules of play come into action. Each large triangle includes nine smaller ones (just as the square grids feature interior boxes); as usual, you must place numbers one to nine in each triangle. But then solvers face some unique (and exciting!) requirements for filling in the edges, for completing the "three legs" of the inner shaded triangle, and for handling the hexagon shapes. Fans of traditional sudoku will find it irresistible! This book is ideal for sudoku fans looking for a new challenge, and a handy pocket-size format those on the go.