Hurwitz numbers and intersections on moduli spaces of curves
  This article is an extended version of preprint math.AG/9902104. We find an explicit formula for the number of topologically different ramified coverings of a sphere by a genus g surface with only one complicated branching point in terms of Hodge integrals over the moduli space of genus g curves with marked points. 
T. Ekedahl, S. Lando, M. Shapiro and A. Vainshtein