Mordell's Pellian equation conjecture

Let dN2d\in\mathbb{N}_{\geq 2} be squarefree, let K=Q(d)K=\mathbb{Q}(\sqrt{d}), let OK\mathcal{O}_K be the ring of algebraic integers of KK, and let ε>1\varepsilon>1 be the fundamental unit of OK\mathcal{O}_K. Set

ω={dif d2,3(mod4),1+d2if d1(mod4).\omega=\begin{cases}\sqrt{d}&\text{if }d\equiv 2,3\pmod 4,\frac{1+\sqrt{d}}{2}&\text{if }d\equiv 1\pmod 4.\end{cases}

Write ε=x+yω\varepsilon=x+y\omega with x,yN0x,y\in\mathbb{N}_0. Mordell's Pellian equation conjecture. If dPd\in\mathbb{P} and d3(mod4)d\equiv 3\pmod 4, then dyd\nmid y. The paper's abstract states that recently discovered counterexamples to Mordell's Pellian equation conjecture are discussed, so its status is refuted.

Sources & referencesView supporting material

Primary source

Andreas Reinhart, “On counterexamples to Mordell's Pellian Equation Conjecture and the AAC-Conjecture: a non-computer based approach”, arXiv:2404.03038 (2025).

Additional references

2 papers in this index state this conjecture (2024). The statement above is taken from the most recent of them; the others are arXiv:2402.09827.

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