Conjectures on radii, densities, and symmetries of maximally circlable circles

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For a nonnegative integer nn, an MC-circle is a largest circle enclosing exactly nn lattice points in its interior, and RnR_n is its radius; an integer is MC if it is maximally circlable and non-MC otherwise. A lattice circle is a circle with at least three lattice points on its circumference. For n≠6n\ne6, let ρn\rho_n be the radius of the largest nn-enclosing lattice circle when one exists, and set ρn=0\rho_n=0 otherwise; a strong MC number is an MC number immediately followed by a non-MC number. MC-circle distribution conjectures. The following assertions hold: for MC numbers k<ℓk<\ell, Rk<RℓR_k<R_\ell; every non-MC n≠6n\ne6 has a largest nn-enclosing lattice circle; the values in {ρn}n≥0\{\rho_n\}_{n\ge0} are pairwise distinct; there are arbitrarily long consecutive sequences of MC numbers and of non-MC numbers; the density of MC numbers is greater than 80%80\%, while that of non-MC numbers is positive and less than 20%20\%; strong MC numbers are infinite and have positive density among MC numbers; every MC-circle of a strong MC number has at least six lattice points on its circumference; the stated majority, minority, and percentage claims about mirror symmetries and axes of symmetry in items (10)--(19) hold exactly as listed in the source. These claims are extrapolated from computations for n<1100n<1100 and remain unresolved in the paper.

References

Primary source

Jianqiang Zhao, “The Largest Circle Enclosing n Lattice Points”, arXiv:2505.06234 (2025).

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