Positive integers are colored either blue or red such that if $a,b$ have the same color and $a-10b$ is a positive integer then $a-10b, a$ have the same color as well. How many such coloring exist?
Source: 239 2015 J3
Tags: combinatorics
Positive integers are colored either blue or red such that if $a,b$ have the same color and $a-10b$ is a positive integer then $a-10b, a$ have the same color as well. How many such coloring exist?