MathDB
max no of marked cells in 20 x 20 board

Source: New Zealand MO 2021 Round 1 p8

September 20, 2021
combinatoricsboard

Problem Statement

Two cells in a 20×2020 \times 20 board are adjacent if they have a common edge (a cell is not considered adjacent to itself). What is the maximum number of cells that can be marked in a 20×2020 \times 20 board such that every cell is adjacent to at most one marked cell?
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