MathDB
2019 Cono Sur Mathematical Olympiad, P3

Source:

August 28, 2019
algebraarithmetic sequencepermutationcono sur

Problem Statement

Let n3n\geq 3 an integer. Determine whether there exist permutations (a1,a2,,an)(a_1,a_2, \ldots, a_n) of the numbers (1,2,,n)(1,2,\ldots, n) and (b1,b2,,bn)(b_1, b_2, \ldots, b_n) of the numbers (n+1,n+2,,2n)(n+1,n+2,\ldots, 2n) so that (a1b1,a2b2,anbn)(a_1b_1, a_2b_2, \ldots a_nb_n) is a strictly increasing arithmetic progression.