MathDB
the numbers form an arithmetic progression

Source: China TST 1994, problem 2

May 17, 2005
functionratioarithmetic sequencealgebrasystem of equationscombinatorics unsolvedcombinatorics

Problem Statement

An nn by nn grid, where every square contains a number, is called an nn-code if the numbers in every row and column form an arithmetic progression. If it is sufficient to know the numbers in certain squares of an nn-code to obtain the numbers in the entire grid, call these squares a key. a.) Find the smallest sNs \in \mathbb{N} such that any ss squares in an nn-code (n4)(n \geq 4) form a key. b.) Find the smallest tNt \in \mathbb{N} such that any tt squares along the diagonals of an nn-code (n4)(n \geq 4) form a key.