MathDB
TOT 1998 Spring OS3 max colours to pain 8x8 chessboard

Source:

May 11, 2020
ChessboardColoringcombinatorics

Problem Statement

What is the maximum number of colours that can be used to paint an 8×88 \times 8 chessboard so that every square is painted in a single colour, and is adjacent , horizontally, vertically but not diagonally, to at least two other squares of its own colour?
(A Shapovalov)