Langford sequences and a product of digraphs
  Skolem and Langford sequences and their many generalizations have applications in numerous areas. The $\otimes_h$-product is a generalization of the direct product of digraphs. In this paper we use the $\otimes_h$-product and super edge-magic digraphs to construct an exponential number of Langford sequences with certain order and defect. We also apply this procedure to extended Skolem sequences. 
Susana-Clara L\'opez and Francesc-Antoni Muntaner-Batle
math.CO