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Hyperbolic expressions of polynomial sequences and parametric number sequences defined by linear recurrence relations of order 2. (English) Zbl 1320.33015

Summary: A sequence of polynomial \(\{a_n(x)\}\) is called a function sequence of order 2 if it satisfies the linear recurrence relation of order 2: \(a_n(x) = p(x)a_{n-1}(x) + q(x)a_{n-2}(x)\) with initial conditions \(a_0(x)\) and \(a_1(x)\). In this paper we derive a parametric form of \(a_n(x)\) in terms of \(e^\theta\) with \(q(x) = B\) constant, inspired by Askey’s and Ismail’s works shown in [R. Askey, Fibonacci and related sequences, Math. Teach. 97, No. 2, 116–119 (2004), ME 2004e.04107], [P. S. Bruckman, Advanced problems and solutions H460, Fibonacci Q. 31, 190–191 (1993)], and [Fibonacci Q. 46–47(2008/2009), No. 2, 167–180 (2009; Zbl 1234.11016)], respectively. With this method, we give the hyperbolic expressions of Chebyshev polynomials and Gegenbauer-Humbert polynomials. The applications of the method to construct the corresponding hyperbolic form of several well-known identities are also discussed in this paper.

MSC:

33C45 Orthogonal polynomials and functions of hypergeometric type (Jacobi, Laguerre, Hermite, Askey scheme, etc.)
05A15 Exact enumeration problems, generating functions
11B39 Fibonacci and Lucas numbers and polynomials and generalizations
12E10 Special polynomials in general fields
39A70 Difference operators

Citations:

Zbl 1234.11016