MathDB

An arrangement of chips in the squares of

n\times n

table is called sparse if every

2\times 2

square contains at most 3 chips. Serge put chips in some squares of the table (one in a square) and obtained a sparse arrangement. He noted however that if any chip is moved to any free square then the arrangement is no more sparce. For what

n

is this possible? Proposed by S. Berlov

Problem Statement