Large-denominator conjecture for continued fractions avoiding squares

Let vv be a non-square integer with v1013v\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.

Sources & referencesView supporting material

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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