An upper bound for third Hankel determinant of starlike functions connected with $$k-$$ k - Fibonacci numbers

Abstract

In this paper, we investigate the third Hankel determinant problem in some classes of analytic functions in the open unit disc connected with k-Fibonacci numbers $$F_{k,n}$$ $$(k>0)$$ . For this, first, we prove a conjecture, posed in Guney et al. (2017), for sharp upper bound of the second Hankel determinant. In the sequel, we obtain another sharp coefficient bound which we apply in solving the problem of the third Hankel determinant for these functions. Finally, we give an upper bound for the third Hankel determinant in this class. The results presented in the present paper have been shown to generalize and improve some recent work of Sokol et al. (2017).