MathDB
Ternary string

Source: Canada Repêchage 2015/7

June 18, 2016
combinatorics

Problem Statement

A (0x,1y,2z)(0_x, 1_y, 2_z)-string is an infinite ternary string such that:

[*] If there is a 00 in position ii then there is a 11 in position i+xi + x,
[*] if there is a 11 in position jj then there is a 22 in position j+yj + y,
[*] if there is a 22 in position kk then there is a 00 in position k+zk + z.

For how many ordered triples of positive integers (x,y,z)(x, y, z) with x,y,z100x, y, z \leq 100 does there exist (0x,1y,2z)(0_x, 1_y, 2_z)-string?