Did you download Strimko Gold when I told you" It's no longer available. However, you can now buy this very cool, colorful version of Sudoku from the famous Grabarchuk family. They're quite prolific when it comes to producing puzzles. See links below. For this volume the specific authors are: Helen, Tanya, Peter & Serhiy.

But let's talk about Strimko here. These puzzles are really not sudoku. They are actually a variation on the famous Latin Square where each row & column has the numbers 1 - whatever, depending on the grid size.  But each string must also contain the same sequence of numbers.
There are 150 puzzles and the grid sizes go up to 7x7.  They're fun!  My only qualm is that it's printed in black and white.  When the app existed, the colors enhanced the overall appearance.   And the Grabarchuks have assured me that the app will reappear soon.

Of the 150 puzzles, I've done about half of them.

https://www.amazon.com/Strimko-Book-Easy-Master-Puzzles/dp/1973162962/ref=sr_1_1"ie=UTF8&qid=1510170615&sr=8-1&keywords=strimko

Other Grabarchuk Family Puzzle Apps
Fish Crackers
Sliding Tiles
icut
Puzzlium

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