A monotonicity property for generalized Fibonacci sequences

T Mansour, M Shattuck - Mathematica Slovaca, 2017 - degruyter.com
T Mansour, M Shattuck
Mathematica Slovaca, 2017degruyter.com
Given k≥ 2, let an be the sequence defined by the recurrence an= α 1 an–1+…+ α kan–k for
n≥ k, with initial values a 0= a 1=…= ak–2= 0 and ak–1= 1. We show under a couple of
assumptions concerning the constants α i that the ratio annan− 1 n− 1 is strictly decreasing
for all n≥ N, for some N depending on the sequence, and has limit 1. In particular, this holds
in the cases when all of the α i are unity or when all of the α i are zero except for the first and
last, which are unity. Furthermore, when k= 3 or k= 4, it is shown that one may take N to be …
Abstract
Given k ≥ 2, let an be the sequence defined by the recurrence an = α1an–1 + … + αkank for nk, with initial values a0 = a1 = … = ak–2 = 0 and ak–1 = 1. We show under a couple of assumptions concerning the constants αi that the ratio $\frac{\sqrt[n]{a_n}}{\sqrt[n-1]{a_{n-1}}}$ is strictly decreasing for all nN, for some N depending on the sequence, and has limit 1. In particular, this holds in the cases when all of the αi are unity or when all of the αi are zero except for the first and last, which are unity. Furthermore, when k = 3 or k = 4, it is shown that one may take N to be an integer less than 12 in each of these cases.
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