The r-circulant Matrices Associated with k-Fermat and k-Mersenne
Numbers
BAHAR KULOĞLU1*, ENGİN ESER2, ENGİN ÖZKAN3
1Department of Mathematics,
Graduate School of Natural and Applied Sciences,
Erzincan Binali Yıldırım University,
Yalnızbağ Campus, 24100, Erzincan,
TURKEY
2Department of Mathematics,
Erzincan Binali Yıldırım University,
Faculty of Art and Sciences,
Erzincan,
TURKEY
3Department of Mathematics,
Faculty of Arts and Sciences,
Erzincan Binali Yıldırım University,
Yalnızbağ Campus, 24100, Erzincan,
TURKEY
*Corresponding Author
Abstract: - In this study, the main goal is to investigate the -circulant matrices of -Fermat and -Mersenne
numbers, then to find eigenvalues, determinants of these matrices, to evaluate their different norms (Spectral
and Euclidean) and finally to find the right and skew-right circulant matrices.
Key-Words: - -Fermat number, -Merssenne number, Norm (Spectral and Euclidean), Eigenvalues,
Circulant matrices
Received: December 11, 2022. Revised: May 27, 2023. Accepted: June 19, 2023. Published: July 24, 2023.
1 Introduction
Prime numbers are numbers that have remained a
mystery throughout human history. Since prime
numbers are generator numbers, people find the
formula for these numbers. The most well-known of
these are Pierre de Fermat and Marin Mersenne.
Fermat numbers included pseudoprimes. Firstly,
Fermat conjectured that all numbers which are
produced by ( is a non-negative integer)
are prime numbers ( must be the power of 2). One
can see easily that the first 5 numbers are prime but
when it comes to the 6th number there is a problem.
Later Euler proved that this number has factors. So,
it was a composite number. Fermat made a
computational mistake. Now it is an open question
that are there any other numbers like this?
Mersenne numbers have the form ( is a
positive integer). These numbers were studied in
ancient times because of their connection to perfect
numbers. Euclid-Euler theorem asserts this
connection.
Later Francois Proth studied Fermat numbers.
He found, [1], the numbers which are a generalized
form of Fermat numbers. They are of form
. Proth numbers are known as -
Fermat numbers. There are restrictions on these
numbers as , where  and is odd
numbers. Here it can be easily seen that the general
forms of Proth numbers without any restrictions are
-Fermat numbers. The first terms of these
numbers are as follows:
3, 5, 13, 17, 41, 97, 113, 193, 241, 257, 353, 449,
577, 641, 673, 769, 929, 1153, 1217, 1409, 1601,
2113, 2689, 2753, 3137, 3329, 3457, 4481, 4993,
6529, 7297, 7681, 7937, 9473, 9601, 9857 (Proth
numbers are referenced in the On-Line
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Encyclopedia of Integer Sequences in OEIS
as A080076, [2].)
In our study we examine -Fermat numbers and
-Mersenne numbers, [3]. -Fermat number
sequence, denoted by , is defined by

-Mersenne number sequence denoted by  is
defined by 
Recurrence relations of these numbers respectively,
 with 
 (1.1)
 with 

The first terms of these numbers are shown in Table
1.
Table 1. Some values for  and .
0
1
3

2
3



0
1

Now we introduce circulant and -cirulant
matrices. Among the subjects of algebra, especially
in linear algebra, these matrices draw attention.
These matrices are used in a number of operations
such as signaling, coding, etc. They are also used in
the field of chemistry, [4]. The study, [5], presented
the visualization of breathing tense while reflecting
atomic velocities on eigenvectors of the circulant
matrix. In, [6], the author's circulant matrices are
used in Hadamard transform spectroscopy and in the
construction of the optimal chemical design. In [7],
the authors presented the quantum optics effects in
quasi-one-dimensional and two-dimensional carbon
materials by the circulant matrix method. In [8], [9],
the authors gave the lower and upper bounds for the
spectral norms of r -circulant matrices and obtained
some bounds related to the spectral norms of
Hadamard and Kronecker products of these matrices
with the Fibonacci and Lucas numbers. Also, they
presented the spectral norms with - Fibonacci and
-Lucas numbers. Circulant matrices are of great
interest among the subjects of algebra, especially in
the field of linear algebra as Algebraic Geometry,
Number Theory, Topleitz operator, etc.
circulant matrices are shown by 󰇛󰇜 or
where represents the size of matrix. Their inverse,
conjugate transposes, sums, and multiplications can
be malleable. For any complex number without
zero, we can define those matrices. We can examine
its eigenvalues, Euclidean norm, spectral norm,
determinants, and inverse. is determined by its
first-row element and . Given  and 
in recurrence relation we obtain its eigenvalues and
determinant.
Circulant matrices and -circulant matrices
including Fibonacci, Pell, Pell-Lucas, etc. numbers
have been of great interest. In several studies,
eigenvalues, determinants, norms, bounds, and
inverses for these matrices are found. For instance,
[10], presented eigenvalues and the determinant of
the right circulant matrices with Pell numbers and
Pell-Lucas numbers. The study, [11], presented
norms for circulant matrices including Fermat and
Mersenne numbers. In, [12], the authors presented
the exact inverse of circulant matrices with Fermat
and Mersenne numbers. In, [13], the author solved
the determinants of these matrices using matrix
decomposition. In, [14], the authors studied the
properties of the -circulant matices involving
Mersene and Fermat numbers. In this study, we
present circulant matrices by using Fermat
and Mersenne numbers. This study is
constructed of three sections. In the first section, we
introduce the Euclidean norm, Hadamard product,
eigenvalues, and determinants of circulant
matices. In second section we define the
circulant matrices involving - Fermat numbers.
We find the eigenvalues, determinants, sum
identities, norms, and the bound for the spectral
norm for the -Fermat -circulant matrices. In the
last section we study -circulant matrices involving
-Mersenne numbers.
Lemma 1.1, [15], [16]. Let 󰇛󰇜 be a matrix.
The Frobenius or Euclidean norm of is defined as



The column norm of is defined as



The row norm of is defined as



The spectral norm of a matrix defined as
󰇛󰇜󰇛󰇜
where 󰇛󰇜 denote the eigenvalues of 󰇛󰇜
and is the conjugate transpose of .
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Matrix has the relationship between the norm
values given below:
(1.2)
Lemma 1.2, [13]. Let 󰇛󰇜
󰇛󰇜is the Hadamard product of A
and B, then we get
󰇛󰇜󰇛󰇜 (1.3)
where 󰇛󰇜
 and
󰇛󰇜

Definition 1.3, [17]. For 󰇝󰇞 a matrix is
said to be -circulant matrix if is of the form
and it is denoted by 󰇛󰇜, where 
󰇛󰇜 is the first-row vector. For
and , the right and skew-right circulant
matrices are desired, respectively.
  
   
 
  
Lemma 1.4, [17]. Let be -circulant matrices
then its eigenvalues


 
where is the th root of unity and is the th root
of r.
Lemma 1.5, [16]. The Euclidean norm of -
circulant matrix is given by
󰇟󰇛󰇜󰇠

 (1.4)
Lemma 1.6, [10]. For any and , we get
󰇛󰇜

 (1.5)
Lemma 1.7, [18]. Determinant of the circulant
matrix is 󰇭

 󰇮


where the entry 󰇝󰇞 is equal to the entry 󰇝
󰇞 for  and 
are the nth
roots of unity. where are th root of .
Using the above lemmas we can calculate the
eigenvalues, the determinant, Euclidean norms, and
bounds for spectral norms of -circulant matrices
involving -Fermat and -Mersenne numbers with
arithmetic indices. We present many new identities
for -Fermat and -Mersenne numbers.
2 -Fermat -circulant Matrix
and be non-negative integers and 󰇝󰇞.
The -circulant matrices -Fermat numbers are
denoted by  and defined as follows:
Definition 2.1 The -Fermat -circulant matrix is
defined as 󰇛󰇜 where first row
vector is 󰇛󰇛󰇜󰇜
i.e., matrix of the form
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
   󰇛󰇜 󰇛󰇜
󰇛󰇜   󰇛󰇜 󰇛󰇜
    
   󰇛󰇜 
(2.1)
Theorem 2.2 The eigenvalues of -Fermat -
circulant matrices  are
󰇛󰇜
󰇛󰇜
󰇛󰇜
where 
Proof. 


󰇛󰇜󰇛󰇜







󰇧󰇛󰇜
 󰇨

󰇧
󰇨


󰇛󰇜
󰇛󰇜󰇛󰇜
for 󰇛󰇜
for 󰇛󰇜
and for 󰇛󰇜
as desired.
Corollary 2.3 For and , we get
eigenvalues for the -Fermat right and skew-right
circulant matrices as follows:

󰇛󰇜
󰇛󰇜
󰇛󰇜
󰇛󰇜
󰇛󰇜

and

󰇛󰇜
󰇛󰇜
󰇛󰇜
󰇛󰇜
󰇛󰇜

where is the nth. the root of -1.
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Theorem 2.4 For a positive integer n, we have
󰇛󰇜

 󰇛󰇜
Proof. To get the desired result, we need to know
that the trace of any given square matrix is equal to
the sum of the eigenvalues of that matrix. In that
case


 


󰇛󰇜

according to the expression given above, this sum is
equal to . In that case
󰇛󰇜

 
󰇛󰇜
as desired.
Theorem 2.5 Determinant of  is given by
󰇛󰇜
󰇡󰇛󰇜
󰇢
Proof. From Lemma 1.7, we get
󰇭

 󰇮


For ,
󰇡󰇛󰇜

 󰇢
󰇡󰇛󰇜󰇢


From Lemma 1.6
󰇛󰇜󰇡󰇛󰇜󰇢
Corollary 2.6 The determinants of the -Fermat
right circulant and skew-right circulant matrices are
given as, respectively
󰇛󰇜󰇡󰇛󰇜󰇢
󰇡󰇛󰇜󰇢
On setting and in Theorem 2.2,
the following sum identities are verified for the -
Fermat numbers.
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

󰇱󰇛󰇛󰇜󰇜 󰇜
󰇛󰇜
󰇛󰇛󰇜󰇜
3 Norm of -Fermat -circulant
Matrices
When we take and , we get

    
    
    
    
From Lemma 3.1, the sum of the squares of the -
Fermat numbers will be used to obtain the norms of
different matrices.
Lemma 3.1 The finite sum of squares of the -
Fermat numbers is given by
󰇛󰇜


󰇛󰇜󰇛󰇜
󰇛󰇜
Proof. 󰇛󰇜󰇛󰇜



 


󰇛󰇜
󰇛󰇜󰇛󰇜
as desired.
Theorem 3.2 The Euclidean norm for the -Fermat
-circulant matrices is given by

󰇛󰇜󰇟󰇛󰇜󰇠


Proof. By Eq. (1.4) we get 
󰇟󰇛󰇜󰇠


󰇛󰇜󰇟󰇛󰇜󰇠


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󰇛󰇜󰇟󰇛󰇜󰇠


󰇛󰇜󰇟󰇛󰇜󰇠


as desired.
Theorem 3.3 The bound for the spectral norm of the
-Fermat -circulant matrices is:
for 󰇛󰇜󰇛󰇜


󰇛󰇜󰇛󰇜
󰇛󰇛󰇜󰇛󰇜󰇜

and for
󰇛󰇜󰇛󰇜

󰇛󰇜󰇛󰇜
Proof. By Eq (1.4), the Euclidean norm is given as

󰇟󰇛󰇜󰇠


Here, we need to examine the proof in 2 stages
according to the state of r.
State 1. If , then from Lemma 3.1 we get

󰇛󰇜



 󰇛󰇜



 
󰇛󰇜󰇛󰇜


which implies

󰇛󰇜󰇛󰇜
and from Eq. (1.2) we get

󰇛󰇜󰇛󰇜
Now to obtain the upper bound for the spectral
norm, we write 
in the form of the Hadamard
product of two matrices.

 
   
    
and
   
  

then clearly 
, where denotes the
Hadamard product. Now,
󰇛󰇜





󰇛󰇜󰇛󰇜
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󰇛󰇜

 


󰇛󰇛󰇜󰇛󰇜󰇜
Thus, by Lemma 1.2, we get 
󰇛󰇜󰇛󰇜
󰇛󰇜󰇛󰇜
󰇛󰇜󰇛󰇜

Hence, we have 󰇛󰇜󰇛󰇜

󰇛󰇜󰇛󰇜
󰇛󰇛󰇜󰇛󰇜󰇜
State 2. If , then from Eq. (1.4) and Lemma
3.1 we get

󰇛󰇜



 
󰇛󰇜󰇛󰇜

󰇛󰇜󰇛󰇜
and from Eq. (1.2) we get

󰇛󰇜󰇛󰇜
We calculate the upper bound for the spectral norm
of 
.
Let
    
   
   
   
and
then clearly 
, where denotes the
Hadamard product. So,
󰇛󰇜


󰇛󰇜

 

󰇛󰇜󰇛󰇜
Hence, by Lemma 1.2, we have

󰇛󰇜󰇛󰇜
󰇛󰇜󰇛󰇜
Thus
󰇛󰇜󰇛󰇜

󰇛󰇜󰇛󰇜
as desired.
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Now we give the relations above for the -
Mersenne numbers.
4 -Mersenne -circulant matrix
and be non-negative integers and 󰇝󰇞.
The -circulant matrices -Mersenne numbers are
denoted by  and defined as follows:
Definition 4.1 The -Mersenne -circulant matrix is
defined as 󰇛󰇜 where the first-row
vector is
󰇛󰇛󰇜󰇜 i.e.,
matrix of the form

   󰇛󰇜 󰇛󰇜
󰇛󰇜   󰇛󰇜 󰇛󰇜
    
   󰇛󰇜 
(4.1)
Theorem 4.2 The eigenvalues of -Mersenne -
circulant matrices  are
󰇛󰇜
󰇛󰇜
󰇛󰇜
where 
Proof. 


󰇛󰇜󰇛󰇜


󰇛󰇜󰇛󰇜




󰇧󰇛󰇜
 󰇨

󰇧
󰇨


󰇛󰇜
󰇛󰇜󰇛󰇜
for 󰇛󰇜
for 󰇛󰇜󰇛󰇜
and for
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󰇛󰇜
as desired.
Corollary 4.3 For and we get
eigenvalues for the -Mersenne right and skew-right
circulant matrices as follows:

󰇛󰇜󰇛󰇜
󰇛󰇜󰇛󰇜
󰇛󰇜
and 
󰇛󰇜󰇛󰇜
󰇛󰇜󰇛󰇜
󰇛󰇜
where is the nth. the root of -1.
Theorem 4.4 For a positive integer n, we have
󰇛󰇜󰇛󰇜


Proof. To get the desired result, we need to know
that the trace of any given square matrix is equal to
the sum of the eigenvalues of that matrix. In that
case,


 󰇛󰇜


According to the expression given above, this sum
is equal to . So
󰇛󰇜

 󰇛󰇜
as desired.
Theorem 4.5 Determinant of  is given by
󰇛󰇜󰇛󰇡󰇛󰇜󰇢
Proof. We can prove it like Theorem 2.5.
Corollary 4.6 The determinants of the -Mersenne
right circulant and skew-right circulant matrices are
given as 󰇛󰇜󰇛󰇡󰇛󰇜󰇢
󰇛󰇡󰇛󰇜󰇢
On setting and in Theorem 4.2,
the following sum identities are verified for the -
Mersenne numbers.
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󰇛󰇜
󰇛󰇜
󰇛󰇜


5 Norm of -Mersenne -circulant
matrices
When we take  and

    
    
    
    
From Lemma 5.1, the sum of the squares of the -
Mersenne numbers will be used to obtain the norms
of different matrices.
Lemma 5.1 The finite sum of squares of the -
Mersenne numbers is given by
󰇛󰇜󰇛󰇜󰇛󰇜

 
Proof. The proof is similar to that of Lemma 3.1.
Theorem 5.2 The Euclidean norm for the -
Mersenne -circulant matrices is given by

󰇛󰇜󰇟󰇛󰇜󰇠


Proof. By Eq. (1.4) we get

󰇟󰇛󰇜󰇠


󰇛󰇜󰇟󰇛󰇜󰇠


󰇛󰇜󰇟󰇛󰇜󰇠


󰇛󰇜󰇟󰇛󰇜󰇠


Theorem 5.3 The bound for the spectral norm of the
-Mersenne -circulant matrices is:
For
󰇛󰇜󰇛󰇜

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󰇛󰇜󰇛󰇜
󰇛󰇛󰇜󰇛󰇜󰇜
and for
󰇛󰇜󰇛󰇜

󰇛󰇜󰇛󰇜
Proof. We can prove it like Theorem 3.3.
6 Conclusion
Based on the Fermat and Mersenne number
sequences with similar recurrences, which have
been studied less, the r-circulant matrices of these
sequences were created. Euclidean, row, and
spectral norms, which are eigenvalues,
determinants, and some special norm values, are
discussed depending on this matrix. In addition, the
lower and upper bounds of these matrices for the
spectral norm were examined in closed form. In
addition, right circulant and skew-right circulant
matrices were examined for 1 and -1 values of
depending on eigenvalues. Finally, some interesting
results and sum properties were given.
More interesting results can be expected by
working with the lesser-known Fermat equation
and the more general form of this equation,
.
References:
[1] Weisstein, Eric W. (2019) "Proth
Number". mathworld.wolfram.com.
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https://oeis.org
[3] Mourad Chelgham and Ali Boussayoud
(2021). On the k-Mersenne–Lucas numbers,
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[4] Min, W., English, B.P., Luo, G. P., Cherayil,
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[17] Cline, R. E., Plemmons, R. J., and Worm, G.
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