Ruin probability in the three-seasonal discrete-time risk model
  This paper deals with the discrete-time risk model with nonidentically distributed claims. We suppose that the claims repeat with time periods of three units, that is, claim distributions coincide at times $\{1,4,7,\ldots\}$, at times $\{2,5,8,\ldots\}$, and at times $\{3,6,9,\ldots\}$. We present the recursive formulas to calculate the finite-time and ultimate ruin probabilities. We illustrate the theoretical results by several numerical examples. 
Andrius Grigutis, Agne\v{s}ka Korvel, Jonas \v{S}iaulys
math.PR