The 18th century Swiss mathematician Leonhard Euler apparently developed the concept of "Latin Squares" where numbers in a grid appear only once, across and up and down. In the late 1970's, Dell Magazines in the US began publishing what we now call Sudoku puzzles using Euler's concept with a 9 by 9 square grid. They called it Number Place, and it was developed by an independent puzzle maker, Howard Garnes.
Each Sudoku has a unique solution that can be reached logically without guessing. Enter digits from 1 to 9 into the blank spaces. Every row must contain one of each digit. So must every column, as must every 3x3 square