Circle SudokuClarity Media provides a wide range of different puzzles that are based either loosely or strongly on the sudoku concept.
These variants are published under a wide range of names by newspapers and magazines, so you may have played them without even realising it!
Circle sudoku - sometimes called ensaimada - has the following elements in common with sudoku: within each circular ring of the puzzle, you must place 1 - 9 once only (or 1 - n where n is the number of concentric circles). However there are a couple of variations, and in one variant it is fairly different in that no number above, below, left or right of any placed number can be that number, one greater or one lower. To put it another way, in one main circle sudoku varint each adjacent number must differ by a value of at least two from its neighbours. This is an interesting variant sudoku puzzle though it is not seen that often in publication.
Below is a sample circle sudoku puzzle. Note that there are eight rings in this puzzle and this is the standard version of circle sudoku, rather than the variant outlined above, so numbers in adjacent cells may be 2,3 or 3,4 for instance.
Sample Circle Sudoku Puzzle
Another similar puzzle you may have seen is spider sudoku, which again displays the sudoku grid in rings rather than on an orthodox grid; this puzzle follows the rules of sudoku more closely and differs mainly in display, with each ring and section containing 1 - 9 once only; there is not normally an equivalent of the box constraint. For more information, take a look at our spider sudoku page.