On the sharp lower bounds of Zagreb indices of graphs with given number of cut vertices

The first Zagreb index of a graph G is the sum of the square of every vertex degree, while the second Zagreb index is the sum of the product of vertex degrees of each edge over all edges. In our work, we solve an open question about Zagreb indices of graphs with given number of cut vertices. The sharp lower bounds are obtained for these indices of graphs in Vn,k, where Vn,k denotes the set of all n-vertex graphs with k cut vertices and at least one cycle. As consequences, those graphs with the smallest Zagreb indices are characterized.