Large-denominator conjecture for continued fractions avoiding squares

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Let vv be a non-square integer with v≥1013v\geq10^{13}. Consider rational numbers with continued fraction expansions

[0;4a1,4a2,…,4an,an+1,1,2],[0;4a_1,4a_2,\ldots,4a_n,a_{n+1},1,2],

where the aia_i are positive integers. Large-denominator continued-fraction conjecture. For every such vv, there exists a coprime positive integer u<vu<v such that

uv=[0;4a1,4a2,…,4an,an+1,1,2].\frac{u}{v}=[0;4a_1,4a_2,\ldots,4a_n,a_{n+1},1,2].

The conjecture is motivated by computation and concerns a family whose denominators have no square values despite having no corresponding local obstruction.

References

Primary source

James Rickards and Katherine E. Stange, “Reciprocity obstructions in semigroup orbits in SL(2, Z)”, arXiv:2401.01860 (2025).

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