MathDB
Double dose of cyanide on day 2

Source: USAMO 2023/5

March 23, 2023
AMCUSA(J)MOUSAMOarithmetic sequencemodular arithmeticprimes

Problem Statement

Let n3n\geq3 be an integer. We say that an arrangement of the numbers 11, 22, \dots, n2n^2 in a n×nn \times n table is row-valid if the numbers in each row can be permuted to form an arithmetic progression, and column-valid if the numbers in each column can be permuted to form an arithmetic progression. For what values of nn is it possible to transform any row-valid arrangement into a column-valid arrangement by permuting the numbers in each row?