MathDB
Social Distancing Kingdom

Source: RMM 2021/5

October 14, 2021
RMM 2021geometrycombinatoricscombinatorial geometryRMM

Problem Statement

Let nn be a positive integer. The kingdom of Zoomtopia is a convex polygon with integer sides, perimeter 6n6n, and 6060^\circ rotational symmetry (that is, there is a point OO such that a 6060^\circ rotation about OO maps the polygon to itself). In light of the pandemic, the government of Zoomtopia would like to relocate its 3n2+3n+13n^2+3n+1 citizens at 3n2+3n+13n^2+3n+1 points in the kingdom so that every two citizens have a distance of at least 11 for proper social distancing. Prove that this is possible. (The kingdom is assumed to contain its boundary.)
Proposed by Ankan Bhattacharya, USA