The exact L(3,2,1)-labeling number of odd 4-valent circulants with steps 1 and 5

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Let n∈Nn\in\mathbb{N} be odd with n≥105n\geq105, and let G=Cn(1,5,n−5,n−1)G=C_n(\\{1,5,n-5,n-1\\}). The invariant λ(3,2,1)(G)\lambda_{(3,2,1)}(G) is the minimum span of an L(3,2,1)L(3,2,1)-labeling of GG, meaning a labeling of the vertices by nonnegative integers such that labels of vertices at distances 11, 22, and 33 differ by at least 33, 22, and 11, respectively.

Exact labeling-number conjecture.

λ(3,2,1)(G)=14.\lambda_{(3,2,1)}(G)=14.

The source constructs an L(3,2,1)L(3,2,1)-labeling with span 1414 for the stated range, while computer tests found no labeling with labels 0,1,…,130,1,\ldots,13 for odd n≤101n\leq101. Thus the conjecture combines the construction with the expected lower bound for all odd n≥105n\geq105.

References

Primary source

Přemysl Holub and Martin Kopřiva, “L(3,2,1)-labelings of three classes of 4-valent circulants”, arXiv:2601.12574 (2026).

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