The combinatorial angle of management of batch processes or job-shop for fine chemicals is presented. Indeed, the order of priority for product recipes, which allows one to determine the first batch to be loaded, has a strong combinatorial aspect. When dealing with stochastic algorithms, this aspect requires a precise and non-redundant numbering of the orders of priority. A fairly complex mathematical study based on a family of pseudo-orthogonal polynomials provides a non-recursive formula easy to implement.