Evaluate $sum_{n=2}^infty frac{ln(n)(-1)^n}{n^2} $
I'm trying to find a closed for for the sum:
$$sum_{n=2}^infty frac{ln(n)(-1)^n}{n^2} $$
It's been proven, $$sum_{n=2}^infty frac{ln(n)(-1)^n}{n} = gammaln(2)-frac{ln(2)^2}{2}$$
Since they're similar, I feel there potentially could be a closed form solution of the first one. I want to know if there is also a closed form solution for the first summation.
I managed to rewrite the first sum as a double integral:
$$-int_0^1int_0^1 frac{ln(x)}{ln(y)}left(frac{1}{1+x}-frac{1}{1+xy} right)dxdy $$
But I don't see any overt way of evaluating it. I've tried differentiating under the integral, but to no avail. I can't think of any change of variables that would help simplify as well.
calculus integration sequences-and-series summation
add a comment |
I'm trying to find a closed for for the sum:
$$sum_{n=2}^infty frac{ln(n)(-1)^n}{n^2} $$
It's been proven, $$sum_{n=2}^infty frac{ln(n)(-1)^n}{n} = gammaln(2)-frac{ln(2)^2}{2}$$
Since they're similar, I feel there potentially could be a closed form solution of the first one. I want to know if there is also a closed form solution for the first summation.
I managed to rewrite the first sum as a double integral:
$$-int_0^1int_0^1 frac{ln(x)}{ln(y)}left(frac{1}{1+x}-frac{1}{1+xy} right)dxdy $$
But I don't see any overt way of evaluating it. I've tried differentiating under the integral, but to no avail. I can't think of any change of variables that would help simplify as well.
calculus integration sequences-and-series summation
4
Well, $sum_{n=2}^infty frac{ln(n)(-1)^n}{n} $ is the derivative of eta funtion in $1$, see here: en.wikipedia.org/wiki/Dirichlet_eta_function#Derivatives. Why not plug $s=2$?
– Zacky
Jan 4 at 15:22
I see thank you
– Tom Himler
Jan 4 at 15:26
2
You're welcome, but there is still some work to do. From here:en.wikipedia.org/wiki/Glaisher%E2%80%93Kinkelin_constant we can find a value for $zeta'(2)$ and we should arrive at: $$sum_{n=2}^infty frac{ln(n)(-1)^n}{n}=eta'(2)=frac{pi^2}{12}left(ln(4pi) -12ln(A) +gammaright)$$
– Zacky
Jan 4 at 15:34
1
Just so you know, in your sum I think you forgot to square the denominator. Right now, the sum reads $eta'(1)$.
– Zachary
Jan 4 at 16:41
From differentiating $eta(s)=(1-2^{1-s})zeta(s)$, we obtain $eta'(s)=zeta(s)2^{1-s}log 2+big(1-2^{1-s}big)zeta'(s)$. However, I am not sure what happens near $s=1$, as the left side should be well defined, but the right side does not seem to be.
– Zachary
Jan 4 at 22:35
add a comment |
I'm trying to find a closed for for the sum:
$$sum_{n=2}^infty frac{ln(n)(-1)^n}{n^2} $$
It's been proven, $$sum_{n=2}^infty frac{ln(n)(-1)^n}{n} = gammaln(2)-frac{ln(2)^2}{2}$$
Since they're similar, I feel there potentially could be a closed form solution of the first one. I want to know if there is also a closed form solution for the first summation.
I managed to rewrite the first sum as a double integral:
$$-int_0^1int_0^1 frac{ln(x)}{ln(y)}left(frac{1}{1+x}-frac{1}{1+xy} right)dxdy $$
But I don't see any overt way of evaluating it. I've tried differentiating under the integral, but to no avail. I can't think of any change of variables that would help simplify as well.
calculus integration sequences-and-series summation
I'm trying to find a closed for for the sum:
$$sum_{n=2}^infty frac{ln(n)(-1)^n}{n^2} $$
It's been proven, $$sum_{n=2}^infty frac{ln(n)(-1)^n}{n} = gammaln(2)-frac{ln(2)^2}{2}$$
Since they're similar, I feel there potentially could be a closed form solution of the first one. I want to know if there is also a closed form solution for the first summation.
I managed to rewrite the first sum as a double integral:
$$-int_0^1int_0^1 frac{ln(x)}{ln(y)}left(frac{1}{1+x}-frac{1}{1+xy} right)dxdy $$
But I don't see any overt way of evaluating it. I've tried differentiating under the integral, but to no avail. I can't think of any change of variables that would help simplify as well.
calculus integration sequences-and-series summation
calculus integration sequences-and-series summation
asked Jan 4 at 15:18
Tom HimlerTom Himler
902213
902213
4
Well, $sum_{n=2}^infty frac{ln(n)(-1)^n}{n} $ is the derivative of eta funtion in $1$, see here: en.wikipedia.org/wiki/Dirichlet_eta_function#Derivatives. Why not plug $s=2$?
– Zacky
Jan 4 at 15:22
I see thank you
– Tom Himler
Jan 4 at 15:26
2
You're welcome, but there is still some work to do. From here:en.wikipedia.org/wiki/Glaisher%E2%80%93Kinkelin_constant we can find a value for $zeta'(2)$ and we should arrive at: $$sum_{n=2}^infty frac{ln(n)(-1)^n}{n}=eta'(2)=frac{pi^2}{12}left(ln(4pi) -12ln(A) +gammaright)$$
– Zacky
Jan 4 at 15:34
1
Just so you know, in your sum I think you forgot to square the denominator. Right now, the sum reads $eta'(1)$.
– Zachary
Jan 4 at 16:41
From differentiating $eta(s)=(1-2^{1-s})zeta(s)$, we obtain $eta'(s)=zeta(s)2^{1-s}log 2+big(1-2^{1-s}big)zeta'(s)$. However, I am not sure what happens near $s=1$, as the left side should be well defined, but the right side does not seem to be.
– Zachary
Jan 4 at 22:35
add a comment |
4
Well, $sum_{n=2}^infty frac{ln(n)(-1)^n}{n} $ is the derivative of eta funtion in $1$, see here: en.wikipedia.org/wiki/Dirichlet_eta_function#Derivatives. Why not plug $s=2$?
– Zacky
Jan 4 at 15:22
I see thank you
– Tom Himler
Jan 4 at 15:26
2
You're welcome, but there is still some work to do. From here:en.wikipedia.org/wiki/Glaisher%E2%80%93Kinkelin_constant we can find a value for $zeta'(2)$ and we should arrive at: $$sum_{n=2}^infty frac{ln(n)(-1)^n}{n}=eta'(2)=frac{pi^2}{12}left(ln(4pi) -12ln(A) +gammaright)$$
– Zacky
Jan 4 at 15:34
1
Just so you know, in your sum I think you forgot to square the denominator. Right now, the sum reads $eta'(1)$.
– Zachary
Jan 4 at 16:41
From differentiating $eta(s)=(1-2^{1-s})zeta(s)$, we obtain $eta'(s)=zeta(s)2^{1-s}log 2+big(1-2^{1-s}big)zeta'(s)$. However, I am not sure what happens near $s=1$, as the left side should be well defined, but the right side does not seem to be.
– Zachary
Jan 4 at 22:35
4
4
Well, $sum_{n=2}^infty frac{ln(n)(-1)^n}{n} $ is the derivative of eta funtion in $1$, see here: en.wikipedia.org/wiki/Dirichlet_eta_function#Derivatives. Why not plug $s=2$?
– Zacky
Jan 4 at 15:22
Well, $sum_{n=2}^infty frac{ln(n)(-1)^n}{n} $ is the derivative of eta funtion in $1$, see here: en.wikipedia.org/wiki/Dirichlet_eta_function#Derivatives. Why not plug $s=2$?
– Zacky
Jan 4 at 15:22
I see thank you
– Tom Himler
Jan 4 at 15:26
I see thank you
– Tom Himler
Jan 4 at 15:26
2
2
You're welcome, but there is still some work to do. From here:en.wikipedia.org/wiki/Glaisher%E2%80%93Kinkelin_constant we can find a value for $zeta'(2)$ and we should arrive at: $$sum_{n=2}^infty frac{ln(n)(-1)^n}{n}=eta'(2)=frac{pi^2}{12}left(ln(4pi) -12ln(A) +gammaright)$$
– Zacky
Jan 4 at 15:34
You're welcome, but there is still some work to do. From here:en.wikipedia.org/wiki/Glaisher%E2%80%93Kinkelin_constant we can find a value for $zeta'(2)$ and we should arrive at: $$sum_{n=2}^infty frac{ln(n)(-1)^n}{n}=eta'(2)=frac{pi^2}{12}left(ln(4pi) -12ln(A) +gammaright)$$
– Zacky
Jan 4 at 15:34
1
1
Just so you know, in your sum I think you forgot to square the denominator. Right now, the sum reads $eta'(1)$.
– Zachary
Jan 4 at 16:41
Just so you know, in your sum I think you forgot to square the denominator. Right now, the sum reads $eta'(1)$.
– Zachary
Jan 4 at 16:41
From differentiating $eta(s)=(1-2^{1-s})zeta(s)$, we obtain $eta'(s)=zeta(s)2^{1-s}log 2+big(1-2^{1-s}big)zeta'(s)$. However, I am not sure what happens near $s=1$, as the left side should be well defined, but the right side does not seem to be.
– Zachary
Jan 4 at 22:35
From differentiating $eta(s)=(1-2^{1-s})zeta(s)$, we obtain $eta'(s)=zeta(s)2^{1-s}log 2+big(1-2^{1-s}big)zeta'(s)$. However, I am not sure what happens near $s=1$, as the left side should be well defined, but the right side does not seem to be.
– Zachary
Jan 4 at 22:35
add a comment |
1 Answer
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The definition of $eta(s)$ is
$$eta(s)=(1-2^{1-s})zeta(s)$$
Take the derivative, and we get by product rule
$$eta'(s)=2^{1-s}ln(2)zeta(s)+(1-2^{1-s})zeta'(s)$$
$eta(s)$ also has the following series representation
$$eta(s)=sum_{n=1}^{infty}frac{(-1)^{n-1}}{n^s}$$
Again, take the derivative
$$eta'(s)=sum_{n=2}^{infty}frac{(-1)^{n}ln(n)}{n^s}$$
Now, we can obtain a close form
$$eta'(2)=sum_{n=2}^{infty}frac{(-1)^{n}ln(n)}{n^2}=2^{1-2}ln(2)zeta(2)+(1-2^{1-2})zeta'(2)$$
Note that
$$zeta'(2)=frac{1}{6}pi^2(-12ln(A)+ln(2pi)+gamma),~zeta(2)=frac{pi^2}{6}$$
$$begin{align}
sum_{n=2}^{infty}frac{(-1)^{n}ln(n)}{n^2}&=2^{-1}ln(2)zeta(2)+(1-2^{-1})zeta'(2)\
&=frac{pi^2}{12}ln(2)+frac{pi^2}{12}(-12ln(A)+ln(2pi)+gamma)\
&=frac{pi^2}{12}(ln(4pi)-12ln(A)+gamma)
end{align}$$
add a comment |
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1 Answer
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The definition of $eta(s)$ is
$$eta(s)=(1-2^{1-s})zeta(s)$$
Take the derivative, and we get by product rule
$$eta'(s)=2^{1-s}ln(2)zeta(s)+(1-2^{1-s})zeta'(s)$$
$eta(s)$ also has the following series representation
$$eta(s)=sum_{n=1}^{infty}frac{(-1)^{n-1}}{n^s}$$
Again, take the derivative
$$eta'(s)=sum_{n=2}^{infty}frac{(-1)^{n}ln(n)}{n^s}$$
Now, we can obtain a close form
$$eta'(2)=sum_{n=2}^{infty}frac{(-1)^{n}ln(n)}{n^2}=2^{1-2}ln(2)zeta(2)+(1-2^{1-2})zeta'(2)$$
Note that
$$zeta'(2)=frac{1}{6}pi^2(-12ln(A)+ln(2pi)+gamma),~zeta(2)=frac{pi^2}{6}$$
$$begin{align}
sum_{n=2}^{infty}frac{(-1)^{n}ln(n)}{n^2}&=2^{-1}ln(2)zeta(2)+(1-2^{-1})zeta'(2)\
&=frac{pi^2}{12}ln(2)+frac{pi^2}{12}(-12ln(A)+ln(2pi)+gamma)\
&=frac{pi^2}{12}(ln(4pi)-12ln(A)+gamma)
end{align}$$
add a comment |
The definition of $eta(s)$ is
$$eta(s)=(1-2^{1-s})zeta(s)$$
Take the derivative, and we get by product rule
$$eta'(s)=2^{1-s}ln(2)zeta(s)+(1-2^{1-s})zeta'(s)$$
$eta(s)$ also has the following series representation
$$eta(s)=sum_{n=1}^{infty}frac{(-1)^{n-1}}{n^s}$$
Again, take the derivative
$$eta'(s)=sum_{n=2}^{infty}frac{(-1)^{n}ln(n)}{n^s}$$
Now, we can obtain a close form
$$eta'(2)=sum_{n=2}^{infty}frac{(-1)^{n}ln(n)}{n^2}=2^{1-2}ln(2)zeta(2)+(1-2^{1-2})zeta'(2)$$
Note that
$$zeta'(2)=frac{1}{6}pi^2(-12ln(A)+ln(2pi)+gamma),~zeta(2)=frac{pi^2}{6}$$
$$begin{align}
sum_{n=2}^{infty}frac{(-1)^{n}ln(n)}{n^2}&=2^{-1}ln(2)zeta(2)+(1-2^{-1})zeta'(2)\
&=frac{pi^2}{12}ln(2)+frac{pi^2}{12}(-12ln(A)+ln(2pi)+gamma)\
&=frac{pi^2}{12}(ln(4pi)-12ln(A)+gamma)
end{align}$$
add a comment |
The definition of $eta(s)$ is
$$eta(s)=(1-2^{1-s})zeta(s)$$
Take the derivative, and we get by product rule
$$eta'(s)=2^{1-s}ln(2)zeta(s)+(1-2^{1-s})zeta'(s)$$
$eta(s)$ also has the following series representation
$$eta(s)=sum_{n=1}^{infty}frac{(-1)^{n-1}}{n^s}$$
Again, take the derivative
$$eta'(s)=sum_{n=2}^{infty}frac{(-1)^{n}ln(n)}{n^s}$$
Now, we can obtain a close form
$$eta'(2)=sum_{n=2}^{infty}frac{(-1)^{n}ln(n)}{n^2}=2^{1-2}ln(2)zeta(2)+(1-2^{1-2})zeta'(2)$$
Note that
$$zeta'(2)=frac{1}{6}pi^2(-12ln(A)+ln(2pi)+gamma),~zeta(2)=frac{pi^2}{6}$$
$$begin{align}
sum_{n=2}^{infty}frac{(-1)^{n}ln(n)}{n^2}&=2^{-1}ln(2)zeta(2)+(1-2^{-1})zeta'(2)\
&=frac{pi^2}{12}ln(2)+frac{pi^2}{12}(-12ln(A)+ln(2pi)+gamma)\
&=frac{pi^2}{12}(ln(4pi)-12ln(A)+gamma)
end{align}$$
The definition of $eta(s)$ is
$$eta(s)=(1-2^{1-s})zeta(s)$$
Take the derivative, and we get by product rule
$$eta'(s)=2^{1-s}ln(2)zeta(s)+(1-2^{1-s})zeta'(s)$$
$eta(s)$ also has the following series representation
$$eta(s)=sum_{n=1}^{infty}frac{(-1)^{n-1}}{n^s}$$
Again, take the derivative
$$eta'(s)=sum_{n=2}^{infty}frac{(-1)^{n}ln(n)}{n^s}$$
Now, we can obtain a close form
$$eta'(2)=sum_{n=2}^{infty}frac{(-1)^{n}ln(n)}{n^2}=2^{1-2}ln(2)zeta(2)+(1-2^{1-2})zeta'(2)$$
Note that
$$zeta'(2)=frac{1}{6}pi^2(-12ln(A)+ln(2pi)+gamma),~zeta(2)=frac{pi^2}{6}$$
$$begin{align}
sum_{n=2}^{infty}frac{(-1)^{n}ln(n)}{n^2}&=2^{-1}ln(2)zeta(2)+(1-2^{-1})zeta'(2)\
&=frac{pi^2}{12}ln(2)+frac{pi^2}{12}(-12ln(A)+ln(2pi)+gamma)\
&=frac{pi^2}{12}(ln(4pi)-12ln(A)+gamma)
end{align}$$
answered Jan 4 at 23:46
LarryLarry
2,0012824
2,0012824
add a comment |
add a comment |
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4
Well, $sum_{n=2}^infty frac{ln(n)(-1)^n}{n} $ is the derivative of eta funtion in $1$, see here: en.wikipedia.org/wiki/Dirichlet_eta_function#Derivatives. Why not plug $s=2$?
– Zacky
Jan 4 at 15:22
I see thank you
– Tom Himler
Jan 4 at 15:26
2
You're welcome, but there is still some work to do. From here:en.wikipedia.org/wiki/Glaisher%E2%80%93Kinkelin_constant we can find a value for $zeta'(2)$ and we should arrive at: $$sum_{n=2}^infty frac{ln(n)(-1)^n}{n}=eta'(2)=frac{pi^2}{12}left(ln(4pi) -12ln(A) +gammaright)$$
– Zacky
Jan 4 at 15:34
1
Just so you know, in your sum I think you forgot to square the denominator. Right now, the sum reads $eta'(1)$.
– Zachary
Jan 4 at 16:41
From differentiating $eta(s)=(1-2^{1-s})zeta(s)$, we obtain $eta'(s)=zeta(s)2^{1-s}log 2+big(1-2^{1-s}big)zeta'(s)$. However, I am not sure what happens near $s=1$, as the left side should be well defined, but the right side does not seem to be.
– Zachary
Jan 4 at 22:35