A note on collections of graphs with non-surjective lambda labelings

  • Authors:
  • John P. Georges;David W. Mauro

  • Affiliations:
  • Department of Mathematics, Trinity College, Hartford, CT;Department of Mathematics, Trinity College, Hartford, CT

  • Venue:
  • Discrete Applied Mathematics
  • Year:
  • 2005

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Abstract

The λ-number of a graph G, denoted λ(G), is the smallest integer k such that there exists a function from V(G) into {0, 1, 2,..., k} under which adjacent vertices receive integers which differ by at least 2 and vertices at distance two receive integers which differ by at least 1. We establish the infinitude of the collection of connected graphs G with fixed maximum degree Δ ≥ 4 and fixed λ-number Δ + t, 1 ≤ t ≤ Δ - 1 such that no λ-labeling of G into {0, 1, 2,...., λ(G)} is surjective. Also, from among graphs with no surjective λ-labelings, we construct connected graphs with maximum degree 3, λ-number 5 and arbitrarily large order.