MathDB
2018 preRMO p26, choose 60 unit squares from a 11 x 11 chessboard

Source:

August 8, 2019
combinatoricsChessboard

Problem Statement

What is the number of ways in which one can choose 6060 unit squares from a 11×1111 \times 11 chessboard such that no two chosen squares have a side in common?