red and blue coloring of cells in triangular cells of equilateral triangle
Source: Mathematics Regional Olympiad of Mexico Center Zone 2020 P1
November 14, 2021
combinatoricsColoringEquilateral
Problem Statement
There is a board with the shape of an equilateral triangle with side divided into triangular cells with the shape of equilateral triangles with side (the figure below shows the board when ). Each and every triangular cell is colored either red or blue. What is the least number of cells that can be colored blue without two red cells sharing one side?
https://cdn.artofproblemsolving.com/attachments/0/1/d1f034258966b319dc87297bdb311f134497b5.png