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JOURNALS // Matematicheskie Zametki // Archive

Mat. Zametki, 1973 Volume 13, Issue 3, Pages 351–357 (Mi mzm7130)

Estimates for the coefficients of univalent functions in terms of the second coefficient

L. P. Il'ina

Leningrad State University, USSR

Abstract: For the coefficients $b_n$ of an odd function $f(z)=z+\sum^\infty_{k=1}b_kz^{2k+1}$, regular in the unit disk, we obtain the estimate
\begin{equation} |b_n|\le\frac1{\sqrt2}\sqrt{1+|b_1|^2}\exp\frac12(\delta+\frac12|b_1|^2), \quad\text{where}\;\delta=0,312, \tag{1} \end{equation}
from which it follows that $|b_n|\le1$, if $|b_1|\le0,524$. It follows from (1) that the coefficients $c_n, n=3, 4\ldots$ of a regular function $f(z)=z+\sum^\infty_{k=2}c_kz^k$, univalent in the unit desk, satisfy
\begin{equation} |b_n|\le\frac1{\sqrt2}\sqrt{1+|b_1|^2}\exp\frac12(\delta+\frac12|b_1|^2), \quad\text{where}\;\delta=0,312, \tag{2} \end{equation}
in particular, $|c_n|\le n$, if $|c_2|\le1,046$.

UDC: 517.5

Received: 04.11.1972


 English version:
Mathematical Notes, 1973, 13:3, 215–218

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