Gauss’s class number one problem for real quadratic fields
Establish the existence of infinitely many real quadratic number fields Q(√d) whose class number equals 1.
References
It was conjectured by Gauss that there are infinitely many real quadratic fields with class number one, which is still open.
— On the simultaneous $3$-divisibility of class numbers of quadruples of real quadratic fields
(2512.11346 - Banerjee et al., 12 Dec 2025) in Section 1 (Introduction)