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Elementary Proof of Yu. V. Nesterenko Expansion of the Number Zeta(3) in Continued Fraction
Advances in Difference Equations volume 2010, Article number: 143521 (2010)
Abstract
Yu. V. Nesterenko has proved that ,
,
,
,
,
, and
for
;
,
, and
,
for
His proof is based on some properties of hypergeometric functions. We give here an elementary direct proof of this result.
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

with We denote by

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


for

for
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

Let

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





Let

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


and Let


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 Then, in view of (2.20),

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


where, as before,

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 Since

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
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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.
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Gutnik, L. Elementary Proof of Yu. V. Nesterenko Expansion of the Number Zeta(3) in Continued Fraction. Adv Differ Equ 2010, 143521 (2010). https://doi.org/10.1155/2010/143521
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Keywords
- Differential Equation
- Partial Differential Equation
- Ordinary Differential Equation
- Functional Analysis
- Functional Equation