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On entire functions from the Laguerre-Polya I class with non-monotonic second quotients of Taylor coefficients
Author(s) -
Thu Hien Nguyen,
Anna Vishnyakova
Publication year - 2021
Publication title -
matematičnì studìï/matematičnì studìï
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.482
H-Index - 8
eISSN - 2411-0620
pISSN - 1027-4634
DOI - 10.30970/ms.56.2.149-161
Subject(s) - laguerre polynomials , quotient , monotonic function , mathematics , taylor series , order (exchange) , function (biology) , combinatorics , class (philosophy) , entire function , pure mathematics , mathematical analysis , finance , evolutionary biology , artificial intelligence , computer science , economics , biology
For an entire function $f(z) = \sum_{k=0}^\infty a_k z^k, a_k>0,$ we define its second quotients of Taylor coefficients as $q_k (f):= \frac{a_{k-1}^2}{a_{k-2}a_k}, k \geq 2.$ In the present paper, we study entire functions of order zerowith non-monotonic second quotients of Taylor coefficients. We consider those entire functions for which the even-indexed quotients are all equal and the odd-indexed ones are all equal:$q_{2k} = a>1$ and $q_{2k+1} = b>1$ for all $k \in \mathbb{N}.$We obtain necessary and sufficient conditions under which such functions belong to the Laguerre-P\'olya I class or, in our case, have only real negative zeros. In addition, we illustrate their relation to the partial theta function.