Jensen Functional, Quasi-Arithmetic Mean and Sharp Converses of Holder's Inequalities

In this article, we give sharp two-sided bounds for the generalized Jensen functional J(n)(f,g,h;p,x). Assuming convexity/concavity of the generating function h, we give exact bounds for the generalized quasi-arithmetic mean A(n)(h;p,x). In particular, exact bounds are determined for the generalized power means in terms from the class of Stolarsky means. As a consequence, some sharp converses of the famous Holder's inequality are obtained.