I call these “Blackjack Puzzles” since they have 21 seed values. (Most of the others on this site have at least 24.) This alone may make the puzzles more difficult. However, apart from that, the difficulty of these puzzles spans the entire range of possible difficulties. Most need just the “standard” solving techniques, but some need the “advanced” solving techniques.
In order to generate these puzzles in a reasonable amount of time, I made a change to my Sudoku program. Before, during puzzle generation, my program chose available cells at random. To speed things up, I added the option to choose from the cells with the greatest number of possibilities. This sped up the generation of Blackjack puzzles by about 15-20 times! This also resulted in more balanced initial patterns. Many of these puzzles have just two or three seed values per group, and most have no empty groups. But in general, this technique also seems to result in fewer really difficult puzzles.
The puzzles are available in printable form as PDF files. Each file contains 100 puzzles, with 2 puzzles per page.
If you really enjoy these puzzles, consider making a contribution to support the continued existence of this web site. Click on the Tip Jar below to make a $15 payment via PayPal. Think of how much you have to pay for Sudoku books in the store. And think about how many puzzles you can download from this site.
Puzzles
Choose puzzle by number, then click on button.| Get Puzzle Set |
Answers
Choose puzzle by number, then click on button.| Get Answers |