Coefficient estimation of a certain subclass of bi-close-to-convex functions analytic in the exterior of the unit disc

Abstract

In this paper, we introduce two new subclasses of biunivalent functions analytic in the exterior of the unitdisc. The bounds obtained for the zeroth , first and second coefficient improves upon earlier known results. The resultsare obtained by refining the well-known estimates for the initial coefficients of the Carthe´odory functions.