The sequences-and-series tag has no wiki summary.

**2**

votes

**1**answer

304 views

### Is it true that $c_0(X)^* = \ell_1(X^*)$ ?

I'm trying to prove this that but I can't . Any help/reference ?

**2**

votes

**0**answers

191 views

### Proving that an increasing iterative sequence increases at a decreasing rate

In this question
Proving a sequence of integrals increases (iterated minimax distributions)
Pietro Majer proved that
$$\int_0^1F_n(x) dx \leq \int_0^1F_{n+1}(x) dx$$ when $$F_n(x) = ...

**9**

votes

**2**answers

318 views

### Finding local patterns in a circular list

Consider a list $\boldsymbol{x}=x_0,x_1,\ldots,x_{n-1}$, which we consider to be circular by taking the subscripts modulo $n$. The entries in the list are distinct integers.
A local pattern is a ...

**0**

votes

**1**answer

401 views

### Sequence of smooth functions converging to sgn(x)

I'm looking for a sequence of smooth functions $f_i(x)$ converging to Sign$(x)$, each of which additionally have the following property:
\begin{equation}
f_i(x_1+x_2) = g_i(x_1, f_i(x_2))
...

**0**

votes

**3**answers

700 views

### Simplifying finite sum over 1/(ax+b)

Can I simplify:
\begin{equation}
\sum_{x=x_0}^{x_1} \frac{1}{ax+b}
\end{equation}

**1**

vote

**1**answer

181 views

### About one series. Are there some related special functions?

Hello,
I have the following series:
$$
\sum_{n=2}^\infty \frac{t^n}{\Gamma(a n)} = ?,\qquad t\ge 0,
$$
where the parameter $a\in (0,1]$, $\Gamma$ is the Gamma function. When $a=1$, the above sum ...

**7**

votes

**2**answers

499 views

### The sequence $a_{n+1}=$ the greatest prime factor of $(xa_n+y)$

Let $\operatorname{ GPF}(n)$ be the greatest prime factor of $n$, eg. $\operatorname{ GPF}(17)=17$, $\operatorname{ GPF}(18)=3$.
Is there a way to prove that the sequence $a_{n+1}=\operatorname{ ...

**5**

votes

**1**answer

493 views

### random hyperharmonic series

The Harmonic Series is defined as:
$\sum_{n} \frac{1}{n}$ where $n=1,2,3,4....$.
This series is known to be divergent.
A generalization of this series can be made by raising each term to $p$:
...

**3**

votes

**0**answers

220 views

### Alternating sums of powers of the lngamma ($\small f_p(x) = \sum \log(k!)^p x^k $ at $\small x=-1$)

I'm still fiddling with this recent question and come to a detail, whether I can find closed forms for the sums of the $\small lngamma() $ function. Precisely
$$ \small f_p(x) = \sum_{k=0}^{\infty} ...

**1**

vote

**0**answers

211 views

### Is there an infinite sequence of positive integers $a_n$ s.t. $\sum_{n=1}^\infty{\frac{1}{a_n}}$ converges and $a_n$ contains arbitrary long arithmetic progressions?

This is somewhat related to Erdős conjecture on arithmetic progressions
Is there an infinite sequence of positive integers $a_n$ s.t. $\sum_{n=1}^\infty{\frac{1}{a_n}}$ converges and $a_n$ ...

**6**

votes

**2**answers

414 views

### Alternating sums of GCDs

The exciting question on alternating sums of binomial coefficients triggered me to ask the following much simpler question (sorry if it is too simple, but I'm not a number theorist, so I must be ...

**36**

votes

**2**answers

3k views

### Alternating sum of square roots of binomial coefficients

Let
$$ c_n = \sum_{r=0}^n (-1)^r \sqrt{\binom{n}{r}}. $$
It is clear that $c_n = 0$ if $n$ is odd. Remarkably, it appears that despite the huge positive and negative contributions in the sum ...

**63**

votes

**7**answers

5k views

### Is $ \sum\limits_{n=0}^\infty x^n / \sqrt{n!} $ positive?

Is $$ \sum_{n=0}^\infty {x^n \over \sqrt{n!}} > 0 $$ for all real $x$?
(I think it is.) If so, how would one prove this? (To confirm: This is the power
series for $e^x$, except with the ...

**3**

votes

**1**answer

312 views

### Products of trigonometric functions with increasing frequencies

I am looking at weighted $L_2$ norms of a class of Littlewood polynomials, related to Walsh and Rademacher functions which made me look for pseudo-closed forms or computationally efficient expressions ...

**4**

votes

**1**answer

418 views

### Complexity of computing expansion of a newform level 18 weight 3 and character [3] - OEIS A116418

I am not familiar with newforms, so this may not make any sense.
OEIS sequence A116418 is Expansion of a newform level 18 weight 3 and character [3]
Numerical evidence suggest that up to $10^5$
$$ ...

**14**

votes

**0**answers

809 views

### Regularizing the divergent sum $1^k + 2^k + \cdots$

EDIT:
Under this "regularization", the harmonic series can be interpreted as $s_{-1}$ and assigned a value $$s_{-1} = \lim_{k \rightarrow 1} \zeta(k) (2-2^k) = -2 \log 2$$
I was looking at ...

**5**

votes

**2**answers

770 views

### Divergence of Dirichlet series

Suppose $s$ is a complex number with $\Re(s) \in (0,1]$ and $\{a_n\}$ is a complex sequence converging to $a \neq 0$. Must the Dirichlet series $$\sum_{n=1}^\infty\frac{a_n}{n^s}$$ diverge?
I asked ...

**4**

votes

**0**answers

749 views

### Has n^2*|sin(n)| limit? [closed]

Is there any sub-sequence $n_k$ of natural numbers such as $\lim(n_k^2|\sin(n_k)|) = 0$ ? when $k$ tends to infinity.
In other words, does $\lim(n^2|\sin(n)|)$ exist (equal to infinity)? or there is ...

**9**

votes

**2**answers

1k views

### Defining the slowest divergent series

This question might seem too fuzzy, and if so, I will be happy to withdraw it. Until then, here it is:
I know that a method of slowing a divergent series of positive reals is to replace the $n$-th ...

**2**

votes

**2**answers

904 views

### Ratio of Sequences Sum Inequality

I have two real sequences $a_1,a_2,\dots,a_n$ and $b_1, b_2, \dots, b_n$, with $a_i > 0$ and $1 \leq b_i < n$, and I'm looking for a lower bound of $\sum_i \frac{a_i}{b_i}$ in terms of $\sum_i ...

**1**

vote

**2**answers

325 views

### Asymptotics of Fourier coefficients of power-type functions

I would like to understand the asymptotic behaviour of the Fourier coefficients of
power type functions
$f(t) = |t|^{-\alpha} 1_{[-\pi, \pi]} \qquad 0 < \alpha<1.$
I suppose this is a classic ...

**1**

vote

**1**answer

214 views

### exponential sum - general cases [closed]

hello community.
I need some help
given $k = \sum A_q e^{ia_q s}$ where $k$, and $s$ is known. Can $A_q$ s now be expressed in terms of $a_q$ .
any help in that direction will be appreciated.

**4**

votes

**0**answers

151 views

### Are there infinite sequences of rational cubes whose first differences are positive squares?

This is related to How many sequences of rational squares are there, all of whose differences are also rational squares?
Are there infinite sequences $a_n$ of rational cubes whose first ...

**1**

vote

**1**answer

308 views

### Limit of an infinite series, related to (generalised Newton's) binomial expansion

How to calculate the infinite sum of the following series, related to binomial expansion for rational number, $r$:
...

**2**

votes

**0**answers

400 views

### How to calculate/approximate expectation of function of a binomial random variable?

Hi,
I am stuck at following problem in my research.
Suppose that $M=m$ is a random variable with binomial distribution with parameters $n,p$. The constants $r$ and $\gamma$ are greater than zero. ...

**0**

votes

**2**answers

246 views

### Summing a function using modulus. [closed]

The problem:
If the infinite sum of a function is known, how to find:
$$\begin{align*}
\sum_{i\equiv 0 \mod m}f(x_0+i)=\\\\ f(x_0)+f(x_0+m)+f(x_0+2m)+f(x_0+3m)+\ldots
\end{align*}$$
And if the ...

**1**

vote

**0**answers

262 views

### Sequences defined as solutions to equations : $u_{n}=v_{n}^n$ [closed]

Hello,
I hope this is the appropriate forum for posting.
For $n$ a positive integer at least equal to $2$, define the two following functions as follows :
$f_{n}(x)=\pi/4 + ...

**2**

votes

**2**answers

334 views

### Inverting an asymptotic series

I have the first few terms of a series of the form,
$y(x)=\ln(x)+x+a_0+\frac{a_1}{x}+\frac{a_2}{x^2}+\cdots$.
Knowing that the inverse $x(y)$ exists, I am looking for method to write x in terms of ...

**2**

votes

**2**answers

851 views

### Sum of products of exponentials and polynomials

Hi,
I am looking for a closed-form expression for the finite sum of the product of an exponential function with a polynomial function --- that is, the sum
...

**1**

vote

**0**answers

219 views

### Applying the ideas of power series to certain convolutions - which identities transfer?

Let's suppose I'm working with some set of functions $f_k(n)$. $f_1(n)$ is essentially the root of my functions, and could be nearly anything, and then $f_k(n) = (f_1(n) * f_{k-1}(n))$ for some ...

**2**

votes

**1**answer

308 views

### differential operator power coefficients

Let $(F(x)\frac{d}{dx})^n=\sum_{i=1}^n H_{n,i}(F, F', F^{(2)}, \ldots , F^{(n)})\frac{d^i}{dx^i}$. I'm curious about the exact formula for $H_{n,i}(y_0, y_1, \ldots , y_n)$. What is known about it?

**4**

votes

**2**answers

606 views

### Proving a sequence of integrals increases (iterated minimax distributions)

I am trying to show that $$\int_0^1F_n(x) dx \leq \int_0^1F_{n+1}(x) dx$$ when $$F_n(x) = (1-(1-F_{n-1}(x))^c)^c$$ and $F_0(x) = x$ and $n$ and $c$ are integers, $n\geq 1$ and $c \geq 2$
Note that ...

**5**

votes

**0**answers

723 views

### Convergent series of primes [closed]

If $f(n)$ is a strictly increasing elementary function from the reals to the reals, and $p(n)$ is the $n$'th prime number. Is there any $f(n)$ such that $\sum_{n=1}^\infty\frac{1}{f(p(n))}$ is ...

**2**

votes

**2**answers

630 views

### Sum of Series Where Exponent is Sum of Arithmetic Progression

Hi,
How do i get the sum of such a sequence:
$1 + x^{-1} + x^{-3} + x^{-6} + ...$
where the exponents are actually sum of arithmetic progression. i.e.
$x^{-0} + x^{-(0 + 1)} + x^{-(0 + 1 + 2)} + ...

**-3**

votes

**2**answers

650 views

### An interesting, simple, sequence - surprised to find little material. [closed]

I've been considering this sequence:
$$1,2,3,6,12,24,48,96,192,...$$
I've generated the sequence from the rule
$$V_n=\sum_{0\leq i \lt n} V_i$$
$$V_0=1; V_1=2V_0=V_0+V_0$$
What interests me most, ...

**6**

votes

**2**answers

245 views

### Repeatedly indexing into an $\infty$-sequence of integers

Suppose one has in hand an infinite sequence $s$ of distinct natural numbers,
for example,
$$s=s_1=(1, 3, 5, 7, 9, 11, 13, 15, 17, 19,\ldots) \;.$$
So this sequence can be considered an injection
...

**2**

votes

**0**answers

512 views

### What square-summable sequences are “sinc-summable”?

$\operatorname{sinc} : \mathbb{R} \to \mathbb{R} \;\;$ is defined by $\;\; \operatorname{sinc}(x) \; = \; \begin{cases} 1 & \text{if }\:\;x=0 \\ \\ \frac{\operatorname{sin}(x)}x & \text{else} ...

**6**

votes

**2**answers

752 views

### Is there a combinatorial interpretation of this triangle sequence? Is there a “simpler” formula?

Hi.
I was wondering about this. I've got this triangle sequence:
$$a_{n,k} = \sum_{1 = m_1 < m_2 < \cdots < m_k = n}\ \prod_{j=2}^k S(m_j, m_{j-1})$$.
where the $S(n, k)$ are Stirling ...

**2**

votes

**1**answer

244 views

### The relative homotopy sets $\pi_1(U_n,U_n/O_n)$ and $\pi_1(U_{2n},U_{2n}/USp_{2n})$

During my research I have recently stumbled upon the problem of finding the relative homotopy sets $\pi_1(U_n,U_n/O_n)$ and $\pi_1(U_{2n},U_{2n}/USp_{2n})$ for $n$ large enough to be in the stable ...

**20**

votes

**3**answers

2k views

### The Wronskian of sin(kx) and cos(kx), k=1…n

What is the determinant of the Wronskian of the functions $\{\cos\ x, \sin\ x, \cos\ 2x, \sin\ 2x,\ldots, \cos\ nx, \sin\ nx\}$? This determinant seems to be an integer, and the sequence starts with ...

**8**

votes

**2**answers

829 views

### What is the series expression for (1+1/x)^x about x = \infty?

This seems like it must have been addressed somewhere already, but I cannot find it in any standard series tables.
I have the equation:
$f(z) = \left(1 + \frac{1}{z}\right)^z$.
What is the general ...

**4**

votes

**2**answers

305 views

### Is there a sufficient criteria to guarantee that $\lim_{n} a_{nn} = \lim_{m} \lim_{n} a_{mn}$ ?

Let $a_{mn}$ be a sequence in some $\mathbb{R}^k$. We know in advance that
$$\lim_{n} ~a_{nn} = L_1, \qquad
\lim_{m}~ \lim_{n} ~a_{mn} = L_2 $$
exist. Is there a sufficient criteria to conclude ...

**2**

votes

**3**answers

2k views

### Elementary proof of the equidistribution theorem

I'm looking for references to (as many as possible) elementary proofs of the Weyl's equidistribution theorem, i.e., the statement that the sequence $\alpha, 2\alpha, 3\alpha, \ldots \mod 1$ is ...

**2**

votes

**2**answers

187 views

### Distribution of $\log_\mu n$ mod 1

If $\langle x\rangle $ is the fractional part of $x$, it is known that for $0<\mu<1$, the sequence $\langle \log_\mu n\rangle _{n=1}^\infty$ is dense in $[0,1]$ but is not uniformly distributed. ...

**7**

votes

**2**answers

770 views

### Exact Value of a Series

It is very easy to show that the series
$$\frac{1-1/2}{1\times2} - \frac{1-1/2+1/3}{2\times3} + \frac{1-1/2+1/3-1/4}{3\times4} - ...$$
i.e.
$$\sum_{n=1}^{\infty} ...

**4**

votes

**0**answers

197 views

### Number of times lead changes in a multi-candidate election (reference-request)

In a two candidate election where votes are distributed uniformly at random between the candidates, the probability that the lead changes when tallying the $i$-th vote is the same as the probability ...

**8**

votes

**4**answers

2k views

### Unique limits of sequences plus what implies Hausdorff?

It is known that there are non-Hausdorff spaces which admit unique limits for all convergent sequence (see here) and it is also known that unique limits for nets implies Hausdorff.
What I am ...

**18**

votes

**3**answers

1k views

### Zeroes of the random Fibonacci sequence

Let X_n be the "random Fibonacci sequence," defined as follows:
$X_0 = 0, X_1 = 1$;
$X_n = \pm X_{n-1} \pm X_{n-2}$, where the signs are chosen by independent 50/50 coinflips.
It is known that ...

**0**

votes

**1**answer

186 views

### Distribution wanted

I have a centered random variables $Y_1,Y_2$ which first 10 moments are given respectively by
$$ 0, 1, 0, 6, 0, 90, 0, 2520, 0, 113400 $$
$$0, 1, 0, 32/3, 0, 36847/100, 0, 436879364/15435, 0, ...

**0**

votes

**0**answers

149 views

### Asymptotic behaviour of a recursively defined sequence

I encounter a problem in which I need to characterize the asymptotic behaviour of a sequence.
$\{s_{n,k}\}$ is a stationary probability distribution, i.e., ...