3. Sudoku is a logic-based, combinatorial number-placement puzzle. The objective is to fill a 9x9 grid with digits so that each column, each row, and each of the nine 3x3 sub-grids that compose the gird contains all of the digits from 1 to 9. The puzzle setter provides a partially completed grid, which typically has a unique solution. “Su” means number in Japanese, and "Doku" refers to the single place on the puzzle board that each number can fit into. Don’t get confused with Sodoku which is a bacterial disease from rat bites and scratches.

4.  During the 18th century, a Swiss mathematician Leonhard Euler developed the concept of "Latin Squares" where numbers in a grid appear only once, across and up and down.  In the late 1970's, Howard Garnes developed what we now call Sudoku puzzles using Euler's concept with a 9 by 9 square grid. They called it Number Place.  The famous Sudoku puzzle came about in the mid-1980s by the president of the Japanese puzzle giant Nikoli, Inc., Mr. Maki Kaji. Nikoli gave the game its current name, and helped refine it by restricting the number of revealed to 30 and having them appear symmetrically. 123 312 231

5.  Sudoku X  Killer Sudoku

6.  Hyper Sudoku  Greater-Than Sudoku

7.  Easy: 36  Medium: 30 1 42735 96542 561947 91 187462 89751 37184 4 127 27 7186 2345 6781 4567 7456 62 615

8.  Hard: 28  Evil: 25 8751 9468 9 617 2674 438 3 3728 4135 49 57 26789 86 2831 93 43726 7 39

9. 2,7,82,3,5 3,6,83,6,8, 9 16,7,86,7,8, 9 4,6,8, 9 81426,97635 7963,6,85421,7,81,8 561947 91 187462 89751 37184 4 23,5 3,6,83,6,8, 9 16,7,86,7,8, 9 4,6,8, 9 81426,97635 7963,6,85421,7,81,8 561947 91 187462 89751 37184 4

10. 2,7,82,3,5 3,6,83,6,8, 9 16,7,86,7,8, 9 4,6,8, 9 81426,97635 7963,6,85421,7,81,8 561947 91 187462 89751 37184 4 2356,86,8,916,7,86,7,8, 9 4,6,8, 9 81426,97635 7963,6,85421,7,81,8 561947 91 187462 89751 37184 4

11. 2,7,82,3,5 3,6,83,6,8, 9 16,7,86,7,8, 9 4,6,8, 9 81426,97635 7963,6,85421,7,81,8 561947 91 187462 89751 37184 4 235681794 81426,97635 7963,6,85421,7,81,8 561947 91 187462 89751 37184 4

12. 2,7,82,3,5 3,6,83,6,8, 9 16,7,86,7,8, 9 4,6,8, 9 81426,97635 7963,6,85421,7,81,8 561947 91 187462 89751 37184 4 235681794 814267635 7963,6,85421,7,81,8 561947 91 187462 89751 37184 4

13. 2,7,82,3,5 3,6,83,6,8, 9 16,7,86,7,8, 9 4,6,8, 9 81426,97635 7963,6,85421,7,81,8 561947 91 187462 89751 37184 4 235681794 81426735 7963,6,85421,7,81,8 561947 91 187462 89751 37184 4

14. 2,7,82,3,5 3,6,83,6,8, 9 16,7,86,7,8, 9 4,6,8, 9 81426,97635 7963,6,85421,7,81,8 561947 91 187462 89751 37184 4 235681794 814297635 796354281 561947 91 187462 89751 37184 4

15. 253681794 814297635 796354281 562813947 439726158 187549362 648972513 375168429 921435876