MathDB
n cells occupied by 0 or 1 arranged into a circle

Source: Austrian Polish 1981 APMC

April 30, 2020
combinatorics

Problem Statement

Let n3n \ge 3 cells be arranged into a circle. Each cell can be occupied by 00 or 11. The following operation is admissible: Choose any cell CC occupied by a 11, change it into a 00 and simultaneously reverse the entries in the two cells adjacent to CC (so that x,yx,y become 1x1 - x, 1y1 - y). Initially, there is a 11 in one cell and zeros elsewhere. For which values of nn is it possible to obtain zeros in all cells in a finite number of admissible steps?