  Let $G$ be a graph with minimum degree at least 2. A set $D\subseteq V$ is a
double total dominating set of $G$ if each vertex is adjacent to at least two
vertices in $D$. The double total domination number $\gamma _{\times 2,t}(G)$
of $G$ is the minimum cardinality of a double total dominating set of $G$. In
this paper, we will find double total domination number of Harary graphs.
