Zaremba’s conjecture on bounded partial quotients
Establish the existence of an absolute constant Z such that every positive integer occurs as the denominator of a reduced rational number whose continued-fraction partial quotients are all at most Z.
References
Another famous conjecture is part of the same general type. There exists a positive constant Z such that every natural number is the denominator of some rational number (in reduced form) whose continued fraction partial quotients are ≤ Z.
                — An illustrated introduction to the arithmetic of Apollonian circle packings, continued fractions, and other thin orbits
                
                (2412.02050 - Stange, 3 Dec 2024) in Section “Orbits of thin groups more generally”