Disjoint union of the same graph In graph theory, the disjoint union of graphs $G_1,\dots,G_n$ is sometimes denoted by $G_1+\cdots+G_n$, or also by $\sum_{i=1}^nG_i$. In case $G_i=G$ for all $1\leq i\leq n$, is there another way to denote this disjoint union $\sum_{i=1}^nG$? Maybe $nG$?
I don't want to introduce a new notation in case there already exists one.
 A: The notation $nG$ is certainly used for the disjoint union of $n$ copies of $G$. Here are some examples.
Definition 1.3.17 in West's Introduction to Graph Theory:

The graph obtained by taking the union of graphs $G$ and $Η$ with disjoint vertex sets is the disjoint union or sum, written $G + H$. In general, $mG$ is the graph consisting of $m$ pairwise disjoint copies of $G$.

Diestel's Graph Theory generally writes out the disjoint union of copies of $G$ without notation, but does use the notation at one point in the middle of another definition:

Let us call a graph $H$ ubiquitous with respect to a relation $\le$ between graphs (such as the subgraph relation $\subseteq $, or the minor relation $\preceq$) if $nH \le G$ for all $n \in N$ implies $\aleph_0 H \le G$, where $nH$ denotes the disjoint union of $n$ copies of $H$.

Also, one of my favorite papers in Ramsey theory, Ramsey theory for multiple copies of graphs by Burr, Erdős, and Spencer, uses the notation extensively because it's all about the Ramsey number $r(mG, nH)$. For example, it proves that $r(mK_3, nK_3) = 3m+2n$ when $m \ge n$ and $m\ge 2$.
