Double dose of cyanide on day 2
Source: USAMO 2023/5
March 23, 2023
AMCUSA(J)MOUSAMOarithmetic sequencemodular arithmeticprimes
Problem Statement
Let be an integer. We say that an arrangement of the numbers , , , in a 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 is it possible to transform any row-valid arrangement into a column-valid arrangement by permuting the numbers in each row?