Numerical semigroups in a problem about economic incentives for   consumers
  Motivated by a promotion to increase the number of musical downloads, we introduce the concept of $C$-incentive and show an algorithm that compute the smallest $C$-incentive containing a subset $X \subseteq {\mathbb N}$. On the other hand, in order to study $C$-incentives, we see that we can focus on numerical $C$-incentives. Then, we establish that the set formed by all numerical $C$-incentives is a Frobenius pseudo-variety and we show an algorithmic process to recurrently build such a pseudo-variety. 
Aureliano M. Robles-P\'erez and Jos\'e Carlos Rosales
math.GR cs.DM math.NT