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Repozytorium publikacji
Politechniki Gdańskiej

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Graphs with isolation number equal to one third of the order

A set D of vertices of a graph G is isolating if the set of vertices not in D and with no neighbor in D is independent. The isolation number of G, denoted by \iota(G) , is the minimum cardinality of an isolating set of G. It is known that \iota(G) \leq n/3 , if G is a connected graph of order n, , distinct from C_5 . The main result of this work is the characterisation of unicyclic and block graphs of order n with isolating number equal to n/3 . Moreover, we provide a family of general graphs attaining this upper bound on the isolation number.

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