Bethe lattice
（重定向自Cayley tree）
![A Bethe lattice with coordination number z = 3](/Images/godic/202501/03/Reseau_de_Bethe.svg4145.png")
A Bethe lattice or Cayley tree (a particular kind of Cayley graph), introduced by Hans Bethe in 1935, is an infinite connected cycle-free graph where each node is connected to z neighbours, where z is called the coordination number. It is a rooted tree, with all other nodes arranged in shells around the root node, also called the origin of the lattice. The number of nodes in the kth shell is given by