Calcudoku Japanese Logic Puzzles: 180 Fun And Challenging 9x9 Logic Puzzles To Make You Smarter in a 6x9 Travel Size Edition/ Great Alternative To Sud (Paperback) (ISBN-13: 9781077874138)

If you enjoy Sudoku and other math logic games, then give Calcudoku a try! This 6x9 size makes it perfect to keep in the car, nightstand, or in your briefcase or purse. It helps make good use of what would otherwise be time spent just surfing on your phone. You don't need to be a mathematician, but you do need to use your analytic and deductive skills.

This book contains 180 puzzles on a 9x9 grid which would considered medium to hard depending on your skill level and familiarity with the puzzle rules.