Enter digits from 1 through n in every row and in every column, such that no row or column contains any digit more than once. Anywhere there are two horizontal or vertical neighbors, one of which is double the other, there is a black dot between them. Anywhere there are two horizontal or vertical neighbors that differ by one, there is a white dot between them. Between 1 and 2 there can be either a black or a white dot. Next to the puzzle the value of n is given. More information.