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12 votes
2 answers
499 views

How to determine the value of $\displaystyle f(x) = \sum_{n=1}^\infty\frac{\sqrt n}{n!}x^n$?

How to determine the value of $\displaystyle f(x) = \sum_{n=1}^\infty\frac{\sqrt n}{n!}x^n$? No context, this is just a curiosity o'mine. Yes, I am aware there is no reason to believe a random power ...
Alma Arjuna's user avatar
  • 3,871
4 votes
1 answer
82 views

Evaluate the following series sum.

Problem I’m trying to evaluate the following series sum \begin{equation} S_{j}(z) = \sum_{k=1}^{\infty} \frac{2 H_{k} z^{k+2}}{(k+1)(k+2)^{j}} \end{equation} Where \begin{equation} H_{k} = \sum_{n=1}^{...
BB_'s user avatar
  • 87
2 votes
1 answer
138 views

Powers of polylogarithms

I would like to take powers of arbitrary order to polylogarithm functions. For instance, given $$ \text{Li}_\alpha(z) = \sum_{k=1}^\infty \frac{z^k}{k^\alpha} $$ I am interested in $$ [\text{Li}_\...
AngusTheMan's user avatar
2 votes
0 answers
154 views

Evaluating a variant of the polylogarithm

Consider the infinite sum : $$\sum_{m=1}^{\infty}\binom{m}{my}\frac{z^{m}}{m^{s}}\;\;\;\;s\in\mathbb{C},\;\;\;\;|z|<\frac{1}{2},\;\;\;\;\;0<y<1$$ I want to evaluate this summation in terms ...
Mohammad Al Jamal's user avatar
5 votes
3 answers
268 views

On the series expansion of $\frac{\operatorname{Li}_3(-x)}{1+x}$ and its usage

Recently I have asked about the evaluation of an integral involving a Trilogarithm $($which can be found here$)$. Pisco provided a quite an elegant approach starting with a functional equation of the ...
mrtaurho's user avatar
  • 16.2k
3 votes
2 answers
185 views

Simple way to evaluate $f(n)= \sum_{r=0}^{\infty}r^n x^r$

Does anyone know a simpler formula than the one below for calculating values of this function for any positive integer n? $$f(n)= \sum_{r=0}^{\infty}r^n x^r$$ Here's the derivation for the best ...
user avatar
2 votes
0 answers
74 views

How can I prove that the following function is increasing in $x \in [0,1]$?

How can I prove that the following function is increasing in $x$: $$\sum_{i=1}^{\infty} x (1-x) ^ {i-1} \log \left (1+ \mu (1-x)^{i-1} \right)$$ where $\mu$ is any non-negative number and $x$ is in $[...
Patrik's user avatar
  • 21
1 vote
0 answers
62 views

Convergence of some sums of complex functions

In the context of the probability theory of rare events i found myself dealing with these series of complex functions: $\sum_{n=1}^\infty(1+n)^{-k}z^{n^2}\\$ with z Complex and k Real. $\sum_{n=1}^\...
fabio's user avatar
  • 11
4 votes
3 answers
170 views

There's a small detail in this proof on why $\sum_{k=1}^{\infty}\frac{1}{k^2} = \frac{\pi^2}{6}$ that I can't figure out

http://www.maa.org/sites/default/files/pdf/upload_library/2/Kalman-2013.pdf Here is a link to the article I have been reading. It's really interesting and easy to follow. What bothers me is a result ...
Nick Freeman's user avatar