- Research Article
- Open Access

# Elementary Proof of Yu. V. Nesterenko Expansion of the Number Zeta(3) in Continued Fraction

- Leonid Gutnik
^{1}Email author

**2010**:143521

https://doi.org/10.1155/2010/143521

© Leonid Gutnik. 2010

**Received: **12 August 2009

**Accepted: **10 January 2010

**Published: **2 March 2010

## Abstract

## Keywords

- Differential Equation
- Partial Differential Equation
- Ordinary Differential Equation
- Functional Analysis
- Functional Equation

## 1. Foreword

Applications of difference equations to the Number Theory have a long history. For example, one can find in this journal several articles connected with the mentioned applications (see [1–8]). The interest in this area increases after Apéry's discovery of irrationality of the number This paper is inspired by Yu.V. Nesterenko's work [9]. My goal is to give an elementary direct proof of his expansion of the number in continued fraction. Let us consider a difference equation

the solutions of this equation with initial values

Then

is a sequence of convergents of the continued fraction

Accoding to the famous result of R. Apéry [10],

where and are solutions of difference equation

with initial values The equality (1.6) is equivalent to the equality

with

where Nesterenko in [9] has offered the following expansion of the number in continued fraction:

with

The halved convergents of continued fraction (1.10) compose a sequence containing convergents of continued fraction (1.8). I give an elementary proof of Yu.V. Nesterenko expansion in Section 2.

## 2. Elementary Proof of Yu. V. Nesterenko Expansion

Instead of expansion (1.10) with (1.11), it is more convenient for us to prove the equivalent expansion

with

Furthermore, to avoid confusion in notations, we denote below for the fraction (2.1) by Let

where values are specified in (1.9), and Then

where and values are specified in (2.2), (1.12), and (1.13). We calculate first and for

Since it follows from (2.2) that

We want to to prove that if then

Note that if then (2.12) follows from (2.6)–(2.10). Therefore, we can consider only Let us consider the following difference equations:

with Then , with representing a fundamental system of solutions of (2.13), and , with representing a fundamental system of solutions of (2.14). Making use of standard interpretation of a difference equation as a difference system, we rewrite the equalities (2.13) and (2.14), respectively in the form

where

with be fundamental matrices of solutions of systems (2.15) and (2.16), respectively. Therefore,

for In view of (2.18) and (2.21), and therefore,

Hence

(see [11]).

Further, we have

Let for In view of (2.16) and (2.18),

In view of (2.22), (2.2), (1.12), (1.13), (2.29), and (2.28), the matrix is a fundamental matrix of solutions of system (2.28). The substitution with for transforms the system (2.28) into the system

with for We prove now that if we take and where

with and then we obtain the equality So, let Then, in view of (2.33),

In view of(1.9)

where Hence, in view of (2.19),

In view of (2.34)–(2.36),

In view of (2.30) and (2.33),

Since

it follows from (2.35), (2.37), and (2.38) that

for We prove by induction now the following equality:

for any In view of (2.25) and (2.32), the equality (2.41) holds for In view of (2.26) and (2.33), the equality (2.41) hold for Let and (2.41) holds for Then, in view of (2.29), (2.40), and (2.21),

So, the equality (2.41) holds for any In view of (2.41),

for and in (1.6) and it follows from (2.43) and (2.44), that

As it is well known, for any there exist and such that

We apply (2.23) now. Let In view of (2.2), (1.12)–(1.13), and (2.45), if then

In view of (2.23), (2.50), and (2.49), if

when In view of (2.45), (2.48), and (2.51), there exist and such that

where So, the equality (2.1) is proved. In view of (2.23),

where

Further, we have

Hence, the series (2.53) is the series of Leibnitz type. Therefore, decreases, when increases in and increases, when increases in

## Declarations

### Acknowledgment

The author would like to express his thanks to the reviewer of this article for his efforts, his criticism, his advices, and indications of misprints. Ravi P. Agarwal had expressed a useful suggestion, which the author realized in foreword and references. He is grateful to him in this connection.

## Authors’ Affiliations

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## Copyright

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