The University of Michigan Combinatorics Seminar


Abstract 

Every character on a graded connected Hopf algebra decomposes uniquely as a product of an even character and an odd character. The aim of this talk is to give explicit formulas for the even and odd parts of the universal character on the Hopf algebra of quasisymmetric functions. They have simple descriptions in terms of Legendre's beta function evaluated at halfintegers, or in terms of bivariate Catalan numbers: Properties of characters and of quasisymmetric functions are then used to derive several interesting identities among bivariate Catalan numbers and in particular among Catalan numbers and central binomial coefficients. The necessary background on quasisymmetric functions and Hopf algebras will be reviewed during the talk. This is joint work with Marcelo Aguiar. 