2021 EGMO P1: {m, 2m+1, 3m} is fantabulous
Source: 2021 EGMO P1
April 13, 2021
EGMO 2021combinatoricsEGMOSets
Problem Statement
The number 2021 is fantabulous. For any positive integer , if any element of the set is fantabulous, then all the elements are fantabulous. Does it follow that the number is fantabulous?