The 2-Rainbow Domination Numbers of [Formula: see text] and [Formula: see text]

A k-rainbow dominating function (kRDF) of G is a function [Formula: see text] for which [Formula: see text] we have [Formula: see text]. The weightw(f) of a function f is defined as [Formula: see text]. The minimum weight of a kRDF of G is called the k-rainbow domination number of G, which is denoted by [Formula: see text]. In this paper, we determine the exact values of the 2-rainbow domination numbers of [Formula: see text] and [Formula: see text]. It follows that [Formula: see text] for graphs [Formula: see text] ([Formula: see text]) and [Formula: see text] ([Formula: see text]), answering in part a question raised by Bresar.