Sudoku is Clapping On The 1 and 3 by Cristopher Moore, App variant is DOMINO


Each row, column, and box contains two 1s, two 3s, and one each of 2, 4, 5, 6, and 7. Cages sum to the totals shown. Digits MAY repeat in cages. Cells separated by a single knight's move (in chess) cannot contain the same digit.