The Lewis octets and the 18‐electron principle are well‐known, and are thought to correspond to filling the (s, p)‐like and (s, p, d)‐like shells, respectively, for an MLn complex. The chapter describes the work of Cui et al, where a new class of Zintl ions, plumbaspherene, Pb2‐12, and stannaspherene, Sn2‐12, were characterized by photoelectron spectroscopy as hosts for building up a new type of endohedral clusters. For finding 32‐electron compounds, the choice of a actinide than thorium would both give some of the required electrons, and more appropriate 5f orbitals, until the 5f electrons strongly localize at Am, or so. The author demonstrates the idea in principle works for the model system [U@Si20]6‐ , and then considers the actinide series [An@Si20]n‐ . 32e magic number is not a coincidence for electrons in a particular quasispherical potential well.