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  • articleNo Access

    Maximum and minimum Sombor index among k-apex unicyclic graphs and k-apex trees

    The Sombor index SO of a graph G is defined as

    SO(G)=uvE(G)dG(u)2+dG(v)2,
    where dG(v) is the degree of the vertex v of G. A k-cone c-cyclic graph is the join of the complete graph Kk and a connected c-cyclic graph. A k-apex tree (respectively, k-apex unicyclic graph) is defined as a connected graph G with a k-subset VkV(G) such that GVk is a tree (respectively, unicyclic graph), but GX is not a tree (respectively, unicyclic graph) for any XV(G) with |X|<k. In this paper, we show the minimal graphs of SO(G) among all k-cone c-cyclic graphs with π as their degree sequence, and determine the extremal values and extremal graphs of SO(G) among k-apex unicyclic graphs and k-apex trees, respectively.

  • articleNo Access

    On general Sombor index of graphs

    In this paper, we extend the recently introduced vertex-degree-based topological index, the Sombor index, and we call it general Sombor index. The general Sombor index generalizes both the forgotten index and the Sombor index. We present the bounds in terms of other important graph parameters for general Sombor index. We also explore the Nordhaus–Gaddum-type result for the general Sombor index. We present further the relations between general Sombor index and other generalized indices: general Randić index and general sum-connectivity index.