Bounds on inverse sum indeg index of graph operations

<p>Let <span class="math inline">\(G = (V(G), E(G))\)</span> be a simple connected graph. The inverse sum indeg index of <span class="math inline">\(G\)</span>, denoted by <span class="math inline">\(\text{ISI}(G)\)</span>, is defined as the sum of the weights <span class="math inline">\(\frac{d(u)d(v)}{d(u) + d(v)}\)</span> of all edges <span class="math inline">\(uv\)</span> of <span class="math inline">\(G\)</span>, where <span class="math inline">\(d(u)\)</span> denotes the degree of a vertex in <span class="math inline">\(G\)</span>. In this paper, we first present some lower and upper bound for <span class="math inline">\(ISI\)</span> index in terms of graph parameters such as maximum degree, minimum degree and clique number. Moreover, we compute <span class="math inline">\(ISI\)</span> index of several graph operations like join, cartesian product, composition, corona and strong product of graphs.</p>