Parity differs from lines to diagonals
Source: Kvant Magazine No. 4 2021 M2647
March 9, 2023
combinatoricsKvant
Problem Statement
For which natural numbers it is possible to mark several cells of an board in such a way that there are an even number of marked cells in all rows and columns, and an odd number on all diagonals whose length is more than one cell?Proposed by S. Berlov