Problem

Source: Baltic Way 2018, Problem 7

Tags: combinatorics, Coloring, graph theory, Graph coloring



On a $16 \times 16$ torus as shown all $512$ edges are colored red or blue. A coloring is good if every vertex is an endpoint of an even number of red edges. A move consists of switching the color of each of the $4$ edges of an arbitrary cell. What is the largest number of good colorings so that none of them can be converted to another by a sequence of moves?