Queens in Exile: Non-attacking Queens on Infinite Chess Boards

Abstract

Number the cells of a (possibly infinite) chessboard in some way with the numbers $0, 1, 2, \ldots$. Consider the cells in order, placing a queen in a cell if and only if it would not attack any earlier queen. The problem is to determine the positions of the queens. We study the problem for a doubly-infinite chessboard of size $\mathbb{Z} \times \mathbb{Z}$ numbered along a square spiral, and an infinite single-quadrant chessboard (of size $\mathbb{N} \times \mathbb{N}$) numbered along antidiagonals. We give a fairly complete solution in the first case, based on the Tribonacci word. There are connections with combinatorial games.