4

Part of 2005 Switzerland - Final Round

Problems(1)

(a+ b)/gcd(a, b) \in M

Source: Switzerland - 2005 Swiss MO Final Round p4

Determine all sets

M

of natural numbers such that for every two (not necessarily different) elements

a, b

M

\frac{a + b}{gcd(a, b)}

M

number theorygreatest common divisorGCD