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Second Hankel determinant of logarithmic coefficients of inverse functions in certain classes of univalent functions

  • Sanju Mandal,
  • Molla Basir Ahamed

摘要

The Hankel determinant \({H}_{\mathrm{2,1}}\left({F}_{f-1}/2\right)\) H 2 , 1 F f - 1 / 2 of logarithmic coefficients is defined as

\({H}_{\mathrm{2,1}}\left({F}_{f-1}/2\right):=\left|\begin{array}{cc}{\Gamma }_{1}& {\Gamma }_{2}\\ {\Gamma }_{2}& {\Gamma }_{3}\end{array}\right|={\Gamma }_{1}{\Gamma }_{3}-{\Gamma }_{2}^{2},\) H 2 , 1 F f - 1 / 2 : = Γ 1 Γ 2 Γ 2 Γ 3 = Γ 1 Γ 3 - Γ 2 2 ,

where \({\Gamma }_{1},{\Gamma }_{2},\) Γ 1 , Γ 2 , and \({\Gamma }_{3}\) Γ 3 are the first, second, and third logarithmic coefficients of inverse functions belonging to the class \(\mathcal{S}\) S of normalized univalent functions. In this paper, we establish sharp inequalities \(\left|{H}_{\mathrm{2,1}}\left({F}_{f-1}/2\right)\right|\le 19/288,\) H 2 , 1 F f - 1 / 2 19 / 288 , \(\left|{H}_{\mathrm{2,1}}\left({F}_{f-1}/2\right)\right|\le 1/144,\) H 2 , 1 F f - 1 / 2 1 / 144 , and \(\left|{H}_{\mathrm{2,1}}\left({F}_{f-1}/2\right)\right|\le 1/36\) H 2 , 1 F f - 1 / 2 1 / 36 for the logarithmic coefficients of inverse functions, considering starlike and convex functions, as well as functions with bounded turning of order 1/2, respectively.