Conjectures on radii, densities, and symmetries of maximally circlable circles
For a nonnegative integer , an MC-circle is a largest circle enclosing exactly lattice points in its interior, and 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 , let be the radius of the largest -enclosing lattice circle when one exists, and set 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 , ; every non-MC has a largest -enclosing lattice circle; the values in 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 , while that of non-MC numbers is positive and less than ; 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 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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