In mathematics, and, in particular, in graph theory, a rooted graph is a mathematical graph in which one node is labelled in a special way to distinguish it from the graph's other nodes. This special node is called the root of the graph.
The number of rooted graphs for 1, 2, ... nodes is 1, 2, 6, 20, 90, 544, ... (sequence A000666 in OEIS)
A special case of interest are rooted trees.