What is the minimal n so that there is a Sudoku board with only n squares filled in that has a unique solution

Answer 1

The maximum number of givens provided while still not rendering the solution unique is four short of a full grid; if two instances of two numbers each are missing and the cells they are to occupy form the corners of an orthogonal rectangle, and exactly two of these cells are within one region, there are two ways the numbers can be assigned. Since this applies to Latin squares in general, most variants of Sudoku have the same maximum. The inverse problem—the fewest givens that render a solution unique—is unsolved, although the lowest number yet found for the standard variation without a symmetry constraint is 17, a number of which have been found by Japanese puzzle enthusiasts, and 18 with the givens in rotationally symmetric cells.

Answer 2

17

Answer 3

I cant give you an answer, because the question dont make sense. But if your asking what is the min. filled square that you can have to figure out the solution it depends on what numbers you put in and where. If thats not the question I'll check back and see.

Answer 4

n=1 has a unique solution and it is minimal, when the Sudoku board is 1 x 1. (I have seen Sudoku in sizes 9x9, 25x25, 4x4)