| Summary: | A connected graph <i>G</i> is said to be a cactus if any two cycles have at most one vertex in common. The multiplicative sum Zagreb index of a graph <i>G</i> is the product of the sum of the degrees of adjacent vertices in <i>G</i>. In this paper, we introduce several graph transformations that are useful tools for the study of the extremal properties of the multiplicative sum Zagreb index. Using these transformations and symmetric structural representations of some cactus graphs, we determine the graphs having maximal multiplicative sum Zagreb index for cactus graphs with the prescribed number of pendant vertices (cut edges). Furthermore, the graphs with maximal multiplicative sum Zagreb index are characterized among all cactus graphs of the given order.
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