I’ve added two new collections of Dinosaur mazes to the puzzle collection, which are great for kids. Each collection contains 50 booklets, with 12 mazes per booklet. Within each booklet, the mazes start out easier, and then get progressively harder. If you’d like to see mazes in other shapes, let me know! Easy Dinosaur Mazes […]

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 […]

One of the most difficult Slitherlink puzzles I publish is the Laves Slitherlink, which you can find in its own collection, as well as in my variety slitherlink collection. I recently helped a reader, Billy, solve one of these monsters, and I thought I’d share the tips here. We explored a handful of advanced solving […]

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 […]

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. This is a tough puzzle, book 7, puzzle 7. It was submitted by Stephen, who got stuck after solving 4 numbers, like so: […]

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. This puzzle is also from Margaret, who got stuck on a Tough puzzle (Tough #4 from book 40). If you’d like to try […]