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A regular hexagon divided into equilateral triangles

Source: Balkan Mathematics Olympiad 2014 - Problem-4

May 4, 2014
geometryperimeterbinomial coefficientscombinatorics proposedcombinatorics

Problem Statement

Let nn be a positive integer. A regular hexagon with side length nn is divided into equilateral triangles with side length 11 by lines parallel to its sides. Find the number of regular hexagons all of whose vertices are among the vertices of those equilateral triangles.
UK - Sahl Khan