Figure 1: A series of Wigner crystal structures showing the arrangement of electrons in a circular island from an occupation number of $N=3$ to $N=100$. The electrons form ring structures as more electrons are added. At $N=15$ an inner ring of five electrons is formed, but at $N=16$ the additional electron is forced to the center to start a new ring. For large $N$, a triangular Wigner lattice forms in the center, while the outer electrons remain in rings.