Density functional study was performed on the stability of InnM (n = 11-15, M = Li, Na, K) clusters. In13M are characterized by electronic shell closure with enhanced stability, larger HOMO-LUMO gap, higher ionization potential, and lower electron affinity as compared with clusters of adjacent sizes, while very similar size dependence was found between InnM and AlnM in their electronic properties, suggesting that In13M be magic clusters and promising as building blocks in developing cluster-assembled materials. The calculated AEA of In-13 is close to that of iodine, implying it would behave like a halogen atom in ionic In13M molecule. (C) 2009 Elsevier B.V. All rights reserved.