MathDB
Combinatorics with prime and chess board

Source: 2024 Turkey EGMO TST P5

February 12, 2024
Prime numbergridcombinatorics

Problem Statement

Let pp be a given prime number. For positive integers n,k2n,k\geq2 let S1,S2,,SnS_1, S_2,\dots, S_n be unit square sets constructed by choosing exactly one unit square from each of the columns from p×kp\times k chess board. If SiSj=1|S_i \cap S_j|=1 for all 1i<jn1\leq i < j \leq n and for any duo of unit squares which are located at different columns there exists SiS_i such that both of these unit squares are in SiS_i find all duos of (n,k)(n,k) in terms of pp.
Note: Here we denote the number of rows by pp and the number of columns by kk.