This genre was developed by Naoki Inaba,
Colour 2 squares black in every row and column. Fill the remaining white squares with the digits 1~N, so that each digit appears once in every row and column. N equals the size of the grid minus 2 (e.g. for the example N = 3). The numbers on the outside indicate the sum of the digits in between the 2 black squares in that row or column.