The science journal Nature reports that a mathematician has proven that it takes 17 clues to make a Sudoku. Gary McGuire of University College Dublin showed this in a proof posted online on January 1st (apparently he wasn’t partying on new year’s eve). This means that sudoku puzzles with 16 or fewer clues do not […]

I just found a book in the Kindle bookstore that (incompetently) rips off some of my sudoku puzzles. The book is called “The Most Difficult and Hardest Sudoku Puzzles” and is “copyrighted” by one Johnny Cohen. Here’s the cover: The cover helpfully informs you that the book is a BEST SELLER. Here’s a sample of […]

At the request of a few persistent (and possibly masochistic) puzzle fans, I’ve added four collections of Hexadecimal Sudoku to the puzzle collection. These are 16 x 16 puzzles that use the 16 hexadecimal digits (0-F), instead of the nine digits used in regular Sudoku puzzles. This is a good puzzle to take on your […]

Troubleshooter #4: XYZ-Wing This is part of a series on puzzle solving techniques. If you are stuck on a particular Krazydad puzzle, drop me a note, and I’ll use this space to help you out. Michael wrote in an email: Dad, Good morning and an early happy thanksgiving. I really enjoy your puzzles and I […]

This is undoubtedly the coolest wood working project I have ever seen. A wooden desk whose drawers emit pipe organ sounds ranging over an octave. Open the doors to play a particular melody, and a secret compartment opens. The password can be changed by turning wood screws on the wooden pneumatic logic board, shown below. […]

I’m currently working on an interactive Sudoku page (to be followed by other puzzles as well). If you’d like to play with a very early “beta” version of it, you’ll find it here. The page is designed to work in modern web browsers (Safari, Chrome, Firefox 4+, IE 9+), and also works on iPads. A […]

The latest addition to my puzzle collection, Galaxies are elegant puzzles in which symmetry forms an essential component. You are presented with a grid containing circles, in seemingly random positions. You fill in the lines of the grid to form an island, or galaxy around each circle. The galaxy shapes must be rotationally (or 180° […]

Eighty-seven year old puzzle constructor Yochanan wrote to tell me he has posted scans of his hand-made crossfigure puzzles. You’ll find 80 puzzles, divided into 4 collections here. I find these puzzles to be excellent. However, because they are scans from a book, it helps to zoom in on each page to make the puzzles […]

Apparently, the paltry few KenKen puzzles published in the Times weren’t enough, so a number of you wrote to me asking for KenKen puzzles. I’m publishing a new kind of puzzle called a Kennie. It’s similar to a KenKen, but has a few minor differences. Kinda like those chocolaty sandwich cookies that aren’t exactly like […]

This weekend, I counted all the words on Project Gutenberg. This has been done before, notably, here. My script crawled most of the English language books on Project Gutenberg (about 20,000 titles), and counted how often each word appears, and how many books each word appears in. The script ran for about 20 hours. You […]