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

From papers

Let nNn\in\mathbb{N} be odd with n105n\geq105, and let G=Cn(1,5,n5,n1)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 n101n\leq101. Thus the conjecture combines the construction with the expected lower bound for all odd n105n\geq105.

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Sources & referencesView supporting material

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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