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Euler-Mascheroni Constant

I am just curious.

Is Euler-Mascheroni constant γ=limn(1kn1klnn)\gamma=\lim_{n\rightarrow\infty}(\sum_{1\le k \le n}\frac{1}{k}-\ln n) rational or irrational? And, how to prove rationality?
(edited 11 years ago)

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It's not known. Now, show that

0lnxex  dx=γ.\displaystyle \int\limits_{0}^{\infty}\frac{ \ln{x}}{e^x}\;{dx} = -\gamma.
(edited 11 years ago)
Reply 2
Can I do something like this:

Define x=limnb(γ1kb1k+lnb)b!n!(n1)n(n+1)2x=\lim_{n\rightarrow \infty} b (\gamma-\sum_{1\le k \le b}\frac{1}{k}+\ln b) b! n! (n-1)^{\frac{n(n+1)}{2}}, assuming nZn\in Z

If γQ\gamma\in Q then a,bZ\exists a,b \in Z s.t. γ=ab\gamma=\frac{a}{b}, b±1b\neq \pm 1

Then

x=a(b!n!(n1)n(n+1)2)b(1kb1klnn)(b!n!(n1)n(n+1)2) x=a(b!n!(n-1)^{\frac{n(n+1)}{2}})-b(\sum_{1\le k \le b}\frac{1}{k}-\ln n )(b! n! (n-1)^{\frac{n(n+1)}{2}}), which, after some evaluation, is an integer.

Consider the definition of γ\gamma

x=b(b+1kn1k)(b!n!(n1)n(n+1)2)=b(hugenumerator)n!(b!)2n!(n1)n(n+1)2 x=b(\sum_{b+1\le k\le n}\frac{1}{k})(b!n!(n-1)^{\frac{n(n+1)}{2}})=b\frac{(huge\quad numerator)}{n!}(b!)^2 n! (n-1)^{\frac{n(n+1)}{2}} and it turns out to be an integer as well.

Can I conclude that the constant in rational?

Note: Typos may exist.

EDIT: Do this step by step is probably less confusing.

Define x=limnb(γ1kb1k+lnb)αx=\lim_{n\rightarrow \infty} b (\gamma-\sum_{1\le k \le b}\frac{1}{k}+\ln b)\alpha, assuming nZn\in Z and α=b!n!(n1)n(n+1)2\alpha=b! n! (n-1)^{\frac{n(n+1)}{2}}

If γ=ab\gamma=\frac{a}{b}

Then
x=limb(ab1kb1k+1k(1)kk(n1)k)α=limaαb((hugenumerator)α)α x = \lim b(\frac{a}{b}-\sum_{1\le k\le b}\frac{1}{k}+\sum_{1\le k\le \infty}\frac{(-1)^k}{k(n-1)^{k}})\alpha=\lim a \alpha-b(\frac{(huge\quad numerator)}{\alpha})\alpha which is an integer assuming nZn\in Z.

Similar procedures but using the definition of the constant which will give a integer as well.

EDIT2: Typo corrected: "nominator" to "numerator"
(edited 11 years ago)
Original post by agostino981
Can I do something like this:

Define x=limnb(γ1kb1k+lnb)b!n!(n1)n(n+1)2x=\lim_{n\rightarrow \infty} b (\gamma-\sum_{1\le k \le b}\frac{1}{k}+\ln b) b! n! (n-1)^{\frac{n(n+1)}{2}}, assuming nZn\in Z

If γQ\gamma\in Q then a,bZ\exists a,b \in Z s.t. γ=ab\gamma=\frac{a}{b}, b±1b\neq \pm 1

Then

x=a(b!n!(n1)n(n+1)2)b(1kb1klnn)(b!n!(n1)n(n+1)2) x=a(b!n!(n-1)^{\frac{n(n+1)}{2}})-b(\sum_{1\le k \le b}\frac{1}{k}-\ln n )(b! n! (n-1)^{\frac{n(n+1)}{2}}), which, after some evaluation, is an integer.

Consider the definition of γ\gamma

x=b(b+1kn1k)(b!n!(n1)n(n+1)2)=b(hugenominator)n!(b!)2n!(n1)n(n+1)2 x=b(\sum_{b+1\le k\le n}\frac{1}{k})(b!n!(n-1)^{\frac{n(n+1)}{2}})=b\frac{(huge\quad nominator)}{n!}(b!)^2 n! (n-1)^{\frac{n(n+1)}{2}} and it turns out to be an integer as well.

Can I conclude that the constant in rational?

Note: Typos may exist.
That didn't make any sense whatsoever. :s-smilie:
Reply 4
Original post by L'art pour l'art
That didn't make any sense whatsoever. :s-smilie:


I initially wanted to prove for irrationality by contradiction, but it turns out to be something like this. By the way, the above "monster" I wrote used Taylor series of logarithm, just too lazy to write all steps.
Original post by agostino981

Define x=limnb(γ1kb1k+lnb)αx=\lim_{n\rightarrow \infty} b (\gamma-\sum_{1\le k \le b}\frac{1}{k}+\ln b)\alpha, assuming nZn\in Z and α=b!n!(n1)n(n+1)2\alpha=b! n! (n-1)^{\frac{n(n+1)}{2}}


You do realise that you have n!(n1)n(n+1)2\displaystyle n! (n-1)^{\frac{n(n+1)}{2}} as nn \to \infty?
Original post by agostino981


hugenominatorhuge\quad nominator


Intriguing, though we know what you meant.
Reply 7
Original post by jack.hadamard
You do realise that you have n!(n1)n(n+1)2\displaystyle n! (n-1)^{\frac{n(n+1)}{2}} as nn \to \infty?


Tends to infinity, but we can't just say it is infinity, because it is never infinity.

EDIT: I may change the factorial to gamma function to consider values of nn other than solely integers.

EDIT2: If nZn\in Z, then xZx\in Z. If nZn\notin Z, then nZn \notin Z, I am kind of stuck here, whether should I conclude that γQ\gamma\in Q.

Original post by ghostwalker
Intriguing, though we know what you meant.


I am too lazy to introduce a new polynomial or something like that.
(edited 11 years ago)
Original post by agostino981

I am too lazy to introduce a new polynomial or something like that.


You missed the point. The word is "numerator", not "nominator". :smile:
Reply 9
Original post by ghostwalker
You missed the point. The word is "numerator", not "nominator". :smile:


lol. Thanks! After all, it is not a word frequently used by me. :P
(edited 11 years ago)
Original post by agostino981
Tends to infinity, but we can't just say it is infinity, because it is never infinity.


What I am saying is that your limit does not make sense. That way, I can prove pretty much everything to be a rational number.
Reply 11
Original post by jack.hadamard
What I am saying is that your limit does not make sense. That way, I can prove pretty much everything to be a rational number.


You mean it doesn't converge?

I took the limit because of the definition of the constant.
(edited 11 years ago)
Original post by agostino981
You mean it doesn't converge?

I took the limit because of the definition of the constant.


He means that your xx\to \infty so you cannot conclude that xZ,x\in\mathbb{Z}, because it isn't once we introduce the limit.
(edited 11 years ago)
Reply 13
Original post by Lord of the Flies
He means that your xx\to \infty so you cannot conclude that xZ,x\in\mathbb{Z}, because it isn't once we introduce the limit (which is required given how you are using that definition of γ\gamma


But at first I have already assumed nZn\in Z as the first case to be considered. I am kind of tired at the moment to do the remaining maths.:tongue:
Original post by agostino981
But at first I have already assumed nZn\in Z as the first case to be considered. I am kind of tired at the moment to do the remaining maths.:tongue:


As long as nZn\in\mathbb{Z} you are fine. But the definition of γ\gamma isn't for some fixed nn, so if you want to exploit it in any viable way you must let nn\to\infty in which case xx is no longer an integer.
Reply 15
Original post by Lord of the Flies
As long as nZn\in\mathbb{Z} you are fine. But the definition of γ\gamma isn't for some fixed nn, so if you want to exploit it in any viable way you must let nn\to\infty in which case xx is no longer an integer.


How about of nZn\notin Z, then xZx\notin Z (Just a claim), can it do the same trick?

EDIT: But isn't this summation only accept nNn\in N(I am not going to consider measure theory)?
(edited 11 years ago)
Original post by agostino981
How about of nZn\notin Z, then xZx\notin Z (Just a claim), can it do the same trick?


No, because then your definition of γ\gamma would make absolutely no sense :wink:

Out of interest, was this attempt inspired by a famous proof of the irrationality of e?
Reply 17
Original post by Lord of the Flies
No, because then your definition of γ\gamma would make absolutely no sense :wink:

Out of interest, was this attempt inspired by a famous proof of the irrationality of e?


But isn't the summation in γ\gamma forces nn to be natural number?

Indeed. And I used the same trick to prove 0n(1)k(k+1)k+1\sum_{0\le n \le \infty}\frac{(-1)^k}{(k+1)^{k+1}} to be irrational. No limit on that one so nothing happens but contradiction, so it is irrational.
(edited 11 years ago)
Original post by agostino981
But isn't the summation in γ\gamma forces nn to be natural number?


It is an infinite series over N\mathbb{N}. I was referring to the sum not making sense if n were not an integer.
Reply 19
Original post by Lord of the Flies
It is an infinite series over N\mathbb{N}. I was referring to the sum not making sense if n were not an integer.


So n is a natural number, so x should be an integer.

EDIT: Measure theory probably works at this moment if n is not a natural number.

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