%0 Journal Article %T The Semigroup of Combinatorial Configurations %A Maria Bras-Amor¨Žs %A Klara Stokes %J Computer Science %D 2009 %I arXiv %X A (v,b,r,k) combinatorial configuration is a (r,k)-biregular bipartite graph with v vertices on the left and b vertices on the right and with no cycle of length 4. Combinatorial configurations have become very important for some cryptographic applications to sensor networks and to peer-to-peer communities. Configurable tuples are those tuples (v,b,r,k) for which a (v,b,r,k) combinatorial configuration exists. It is proved in this work that the set of configurable tuples with fixed r and k has the structure of a numerical semigroup. The numerical semigroup is completely described for r=2 and r=3. %U http://arxiv.org/abs/0907.4230v3