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Some properties of the generalized Fibonacci and Lucas sequences related to the extended Hecke groups
Journal of Inequalities and Applications volume 2013, Article number: 398 (2013)
Abstract
In this paper, we define a sequence, which is a generalized version of the Lucas sequence, similar to the generalized Fibonacci sequence given in Koruoğlu and Şahin in Turk. J. Math. 2009, doi:10.3906/mat-0902-33. Also, we give some connections between the generalized Fibonacci sequence and the generalized Lucas sequence, and we find polynomial representations of the generalized Fibonacci and the generalized Lucas sequences, related to the extended Hecke groups given in Koruoğlu and Şahin in Turk. J. Math. 2009, doi:10.3906/mat-0902-33.
MSC:20H10, 11F06.
Dedication
Dedicated to Professor Hari M Srivastava
1 Introduction
In [1], Hecke introduced groups , generated by two linear fractional transformations
where λ is a fixed positive real number. Hecke showed that is discrete if and only if , , , or . These groups have come to be known as the Hecke Groups, and we will denote them , for , , respectively. The Hecke group is the Fuchsian group of the first kind when or , and is the Fuchsian group of the second kind when . In this study, we focus on the case , . The Hecke group is isomorphic to the free product of two finite cyclic groups of orders 2 and q, and it has a presentation
The first several of these groups are (the modular group), , , and . It is clear that , for . The groups and are of particular interest, since they are the only Hecke groups, aside from the modular group, whose elements are completely known (see, [3]).
The extended Hecke group, denoted by , has been defined in [4] and [5] by adding the reflection to the generators of the Hecke group . The extended Hecke group has a presentation
The Hecke group is a subgroup of index 2 in . It is clear that when and (the extended modular group ).
Throughout this paper, we identify each matrix A in with −A, so that they each represent the same element of . Thus, we can represent the generators of the extended Hecke group as
In [6], Koruoglu and Sahin found that there is a relationship between the generalized Fibonacci numbers and the entries of matrices representations of some elements of the extended Hecke group . For the elements
in , then the k th power of h and f are
where , , and for ,
For all ,
Notice that this real numbers sequence is a generalized version of the common Fibonacci sequence. If , this sequence coincides with the Fibonacci sequence.
The Fibonacci and the Lucas sequence have been studied extensively and generalized in many ways. For example, you can see in [7–12]. In this paper, firstly, we define a sequence , which is a generalization of the Lucas sequence. Then we give some properties of these sequences and the relationships between them. To do this, we use some results given in [13–15]. In fact, in [14] and [15], Özgür found two sequences, which are the generalization of the Fibonacci sequence and the Lucas sequence, in the Hecke groups , real. But the Hecke groups are different from the Hecke groups , , , .
2 Some properties of generalized Fibonacci and generalized Lucas sequences
Firstly, we define a sequence by
for , where , .
Proposition 1 For all ,
Proof To solve (6), let be a characteristic polynomial . Then we have the equation
The roots of this equation are
Using these roots , we can find a general formula of the general term . If we write as combinations of the roots , then we have
To determine constants A and B, we use two boundary conditions and , thus,
So,
Then we obtain the formula of as
This completes the proof. □
Notice that this formula is a generalized Lucas sequence. If (the modular group case ), we get the Lucas sequence.
Now, we have two sequences and , which are generalizations of the Fibonacci and the Lucas sequences. Let us write out the first 8 terms of and .
Here, it is possible to extend and backward with the negative subscripts. For example, , , , and so on. Therefore, we can deduce that
and
The sequences and have some similar properties of the Fibonacci and the Lucas numbers and . Now, we investigate some properties of these sequences and .
Proposition 2
Proof We will use induction on k. For , we have
For , we get
Now let us assume that the proposition holds for . We show that it holds for . By assumption, we have
From (3), we obtain
Then we get
Similarly, it can be shown that
□
Proposition 3
Proof We will use the induction method on k. If , then
We suppose that the equation holds for , i.e.,
Now, we show that the equation holds for . Then we have
□
Proposition 4
Proof For , we have
For , we have
Now, we assume that the proposition holds for . We show that it holds for . By assumption, we have
Then we find
□
Proposition 5
Proof We will use induction on k. For , we find
For , we get
Now, let us suppose that the proposition holds for . We show that it holds for . By assumption, and . Hence we get
□
Proposition 6
Proof We will use the induction method on k. For , we have
For , we have
We suppose that the equation holds for , i.e.,
Now, we show that the equation holds for . By equalities (3), (9) and (10),
□
Proposition 7
Proof Using (10) and the definitions of and , we have
In [10], Yayenie and Edson obtained a generalization of Cassini’s identity for the positive real numbers a and b. If we take and in generalized Cassini’s identity, we get
and so,
□
Proposition 8
Proof We will use the induction method on k. For , we have
For , we have
Now, we assume that the proposition holds for . We show that it holds for . From assumption , and, thus,
□
Proposition 9
Let m be fixed. We will use the induction method on k. For , we have
since and . For , we find
since and . Now, we assume that the proposition holds for . We show that it holds for . By assumption,
and
Thus, we have
Now, we give a formula for and .
Proposition 10 For all ,
and
Proof Let k be even. By (4),
Similarly, if k is odd, then we get
□
Proposition 11
and
Proof From (3), we have
and so,
If we sum both sides, then we obtain
Since and , we have
Similarly, it is easily seen that
□
3 Polynomial representations of and
Before we find the polynomial representations of and , note the following identities
and
Theorem 1 Let denote the generalized Fibonacci sequence. Then, the polynomial representations of and are
and
Proof We will use the induction method on k. For , we have , and for , we have . Now, suppose that the equality is true for . We will show that it holds for . By assumption,
and
From (9), we have , and by definition of , we get
From (21), we get
Now, we compute . By definition of , we get
From (22), we get
□
Theorem 2 Let denote the generalized Lucas sequence. Then, the polynomial representations of and are
and
Proof From (10), it is easy to find the polynomial representations of and . □
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İkikardes, S., Sarıgedik, Z. Some properties of the generalized Fibonacci and Lucas sequences related to the extended Hecke groups. J Inequal Appl 2013, 398 (2013). https://doi.org/10.1186/1029-242X-2013-398
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DOI: https://doi.org/10.1186/1029-242X-2013-398