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It takes 17 clues to make a Sudoku

Tuesday, January 10th, 2012

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 […]

Dumb Ripoff Alert

Friday, January 6th, 2012

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 […]

Hexadecimal Sudoku

Tuesday, December 20th, 2011

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 […]

Sudoku Troubleshooter #4 – XYZ-Wing

Thursday, November 24th, 2011

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 […]

Kagen Schaefer’s Pipe Organ Desk

Wednesday, September 21st, 2011

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. […]

Interactive Sudoku Beta

Thursday, September 8th, 2011

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 […]

Galaxy Puzzles

Saturday, August 28th, 2010

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° […]

Yochanan’s Crossfigure Puzzles

Friday, August 13th, 2010

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 […]

Hey KenKen fans!! Meet Kennie…

Friday, August 6th, 2010

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 […]

Mining juicy words

Monday, March 22nd, 2010

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 […]