Normal sudoku rules apply. The nine marked cells contain the digits 1ā9, each exactly once. If a marked cell contains the digit N, then every vertical group of N consecutive cells in its column has remainders 0, 1, ..., Nā1, in some order, when its digits are divided by N. Such a group may start anywhere in the column; it does not need to contain the marked cell. For example, if a marked cell contains 4, then every four consecutive cells in its column have remainders 0, 1, 2, 3 modulo 4, in some order.