MathDB
Two-side grid with numbers

Source: St. Petersburg 2023 9.4=10.4

August 12, 2023
combinatorics

Problem Statement

One side of a square sheet of paper is colored red, the other - in blue. On both sides, the sheet is divided into n2n^2 identical square cells. In each of these 2n22n^2 cells is written a number from 11 to kk. Find the smallest kk,for which the following properties hold simultaneously: (i) on the red side, any two numbers in different rows are distinct; (ii) on the blue side, any two numbers in different columns are different; (iii) for each of the n2n^2 squares of the partition, the number on the blue side is not equal to the number on the red side.