# Questions tagged [closed-form-expressions]

For questions that specifically ask for determining a closed form of equations, integrals etc.

198
questions

2
votes

1
answer

102
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### Exact calculations with Moyal product by "Bopp Shift"

I'm now working on my Phd thesis on the area of deformation quantization and field theory. After doing all the "ground work" (definitions, motivations, basics of the theory etc) I have now ...

3
votes

1
answer

271
views

### How can I verify this family of values for hypergeometric functions?

This Wolfram MathWorld page on hypergeometric functions states that
An infinite family of rational values for well-poised hypergeometric functions with rational arguments is given by $$_kF_{k-1}\left[...

5
votes

0
answers

86
views

### Ratio of theta functions as roots of polynomials

I already asked the same question here, but received no answer. I did some little progress and so I'm asking again.
I was playing with the theta functions with argument $ z = 0 $
$ \vartheta_2(q) =\...

2
votes

0
answers

88
views

### Closed form from a slightly modified recursion for transposed Catalan triangle

Let $a_1(n)$ be A000108, i.e. Catalan numbers. Here
$$
a_1(n)=\frac{1}{n+1}\binom{2n}{n}
$$
Let $a_2(n)$ be A059715, i.e. number of multi-directed animals on the triangular lattice. From OEIS page we ...

2
votes

0
answers

87
views

### Ratio of theta function derivatives with theta function

I have the following ratios I want to compute.
$$ \frac{ \left( \frac{\partial \vartheta_3(v, q)}{\partial v} \right)^2 }{C + \left(\vartheta_3(v, q)\right)^2 }, $$
where $C$ is a constant.
$$ \frac{ \...

0
votes

0
answers

36
views

### Summation of the following form with non-integer n

I have the following function:
$$ G(z) = \sum_{j = 0}^{\infty} \frac{\Gamma(1 + n) z^j}{j ! (\Lambda + jC)^{n+1}} $$
If $n \quad \epsilon \quad \mathbb{Z}^{+} $, the above function can be ...

2
votes

1
answer

156
views

### Is this integral solvable analytically?

I have this integral that comes from my research with some Fourier Transforms of spectrum functions:
$$ G(\tau) = \int_{0}^{\infty} e^{-\Lambda x} x^n e^{i \tau ( c_1 - c_2 e^{-c_3 x} ) } dx $$
where $...

4
votes

1
answer

164
views

### On four Ramanujan-type "Legendrian" sequences with a 3-term recurrence?

I. Recurrences
In a previous post, it was mentioned how Almkvist-Zudilin did a computer search for solutions to the recurrence relation,
$$(n+1)^3s_{n+1}=(2n+1)(an^2+an+b)s_n+c\,n^3s_{n-1}$$
within a ...

0
votes

0
answers

97
views

### Simplification of summation and reverse search

Let $f(n)$ be an arbitrary function such that $f(n)\in\mathbb{Z}$.
Let $b(n)$ be an integer sequence such that
$$b(2^m(2n+1))=\sum\limits_{k=0}^{m}f(m-k)b(2^kn), b(0)=1$$
Let $s(n,m)$ be an integer ...

8
votes

2
answers

558
views

### On Zagier's missing continued fraction with multiple limits?

I. Zagier's continued fraction
As pointed out by Gorodetsky in his answer, Zagier evaluated the continued fractions associated with his six sporadic sequences excepting the one for $(-9,-3,-27)$. Let $...

6
votes

1
answer

241
views

### On the continued fractions using Cooper's sequences $s_7,\, s_{10},\, s_{18}$ and the Zudilin-Cohen sequence

In a previous MO post, H. Cohen suggested Gorodetsky's 2021 paper which discussed $6+6+3=15$ "sporadic sequences". The first 6 are Zagier's sporadic sequences, the second 6 are by Almkvist-...

10
votes

2
answers

620
views

### On 12 cfracs: for Catalan's $K$, Gieseking's $\kappa$, and $\pi^2$, $\pi^3$, plus three for $\zeta(3)$ using Zagier's "six sporadic sequences"

I. Some functions
As these will be used in the continued fraction evaluations below, recall the Riemann zeta function $\zeta(s),$ and Dirichlet beta function $\beta(s),$
$$\beta(s) = \sum_{n=1}^\infty\...

1
vote

0
answers

36
views

### Sequences that sum up to $\frac{m^{n+1}}{n+1}\binom{2n}{n}{}_2F_1(1,n+\frac{1}{2}; n+2; -4m(m-1))$

Let $a(n,m)$ be an integer sequence such that
$$a(n,m)=\frac{m^{n+1}}{n+1}\binom{2n}{n}{}_2F_1(1,n+\frac{1}{2}; n+2; -4m(m-1))$$
Let
$$\ell(n)=\left\lfloor\log_2 n\right\rfloor$$
$$f(n)=n-2^{\ell(n)}$$...

0
votes

0
answers

34
views

### $\frac{m(m+k+1)^n+k}{m+k}$ as closed form for subsequence of the partial sums

Let $a(n,m,k)$ be an integer sequence such that
$$a(n,m,k)=\frac{m(m+k+1)^n+k}{m+k}$$
There are many sequences in the OEIS that are special cases of a given sequence family:
$a(n,1,1)$ - A007051
$a(n,...

0
votes

0
answers

40
views

### Product as closed form for subsequence of the partial sums

Let $a(n,m,k)$ be an integer sequence such that
$$a(n,m,k)=\prod\limits_{q=0}^{n-1}\sum\limits_{i=0}^{m-1}\sum\limits_{j=0}^{m-i-1}\binom{i+j-1}{j}k^{i+j}q^i$$
Let
$$\ell(n,m)=\left\lfloor\log_m n\...

4
votes

2
answers

490
views

### Finding a sextic analogue to the solvable octic $\frac{(x + 1)^6(x^2 + x + 7)}x = -k^3$ where $e^{(\pi/3)\sqrt{d}}\approx k^3+41.999999999999\dots$

I. Degree 8
Assume the $j_i$ to be free parameters. The following octics in $x$ belong to $8T43,$ have group $\text{PGL}(2,7)$, and order $2\times168 = 336.$
\begin{align}
{j_1}\; &=\frac{(x^2 + ...

0
votes

0
answers

64
views

### On a generalization of A113227 as a subsequence of the partial sums

This question is just a generalization of the one of my previous questions.
Let
$$a(n,m,k)=\sum\limits_{i=1}^{n}u(n,m,k,i)$$
where
$$u(n,m,k,i)=u(n-1,m,k,i-1)+(m-1)(i+k-1)\sum\limits_{j=i}^{n-1}u(n-1,...

4
votes

0
answers

80
views

### Closed form for subsequence of the partial sums of generalized A329369

Let $a(n,m,k)$ be an integer sequence such that
$$a(n,m,k)=\sum\limits_{i=0}^{n}{n\brace i}(m-k)^{n-i}\prod\limits_{j=0}^{i-1}(kj+1)$$
Here ${n\brace k}$ is the Stirling number of the second kind.
...

1
vote

1
answer

169
views

### Analytic expression for $\int_0^\infty \mathrm{d}p\frac{e^{-p \sin (\phi )} \sin (p \cos (\phi ))}{p \left(e^{c p}+1\right)}$

I am looking for ways to do this integration analytically
\begin{equation}
\int_0^\infty \mathrm{d}p\frac{e^{-p \sin (\phi )} \sin (p \cos (\phi ))}{p \left(e^{c p}+1\right)}
\end{equation}
For ...

17
votes

1
answer

787
views

### On the solvable septic quadrinomial $x^7-7x^4-14x^3-7=0$?

The concept of sparse polynomials has its place, and solvable but irreducible quadrinomial examples such as,
$$x^7-7x^4-14x^3-7=0$$
$$x^8+x^7+29x^2+29=0$$
$$x^9-27x^4-9x^3-9^2=0$$
$$x^{12}-36x^5-12x^3-...

1
vote

0
answers

81
views

### Derive a closed-form expression of this recursive formula

$$\begin{equation}
S(r,k) = f(r)S(0,k-1) + g(r)S(r+1,k-1)
\end{equation}\ ,$$
where $r=0,1,2,\dots$ and $k=1,2,3,\dots$ . Also, $0<f(r)<1$ is an increasing function and $0<g(r)<1$ is a ...

1
vote

1
answer

110
views

### Coefficients of number of the same terms which are arising from iterations based on binary expansion of $n$

Let
$$\ell(n)=\left\lfloor\log_2 n\right\rfloor$$
Let
$$T(n,k)=\left\lfloor\frac{n}{2^k}\right\rfloor\operatorname{mod}2$$
Here $T(n,k)$ is the $(k+1)$-th bit from the right side in the binary ...

1
vote

0
answers

116
views

### $\sin(\frac{\pi}{p}) $ not expressible by positive radicals and $\sin(\frac{\pi}{q_i})$?

We have the following identities:
$\sin(\frac{\pi}{1})=0$
$\sin(\frac{\pi}{2})=1$
$\sin(\frac{\pi}{3})=\frac{\sqrt{3}}{2}$
$\sin(\frac{\pi}{4})=\sqrt{\frac{1}{2}}$
Lets start with a definition.
Rules ...

3
votes

1
answer

239
views

### Integrating $\int_0^\infty \sqrt x e^{-4/3x^{3/2}}\left(\int_0^x \operatorname{Ai}(t)dt\int_0^x \operatorname{Bi}(t)dt\right)dx$

Show that
$$I= \int_0^\infty \sqrt x e^{\large -4/3x^{3/2}}\left(\int_0^x \operatorname{Ai}(t)dt\int_0^x \operatorname{Bi}(t)dt\right)dx$$
$$=\frac{1}{3}-\frac{\sqrt[3]{2\sqrt 3+3}+\sqrt[3]{2\sqrt 3-3}...

3
votes

1
answer

347
views

### Using the Lehmer quintic to solve $11$-degree equations and higher?

(This is a natural continuation of a previous post.)
I. Quintic method
Given the Lehmer quintic,
$$x^5 + n^2x^4 - (2n^3 + 6n^2 + 10n + 10)x^3 + (n^4 + 5n^3 + 11n^2 + 15n + 5)x^2 + (n^3 + 4n^2 + 10n + ...

0
votes

0
answers

68
views

### How to perform this integral to get a closed/ semi closed form

I want to get a closed/ semi-closed form of the integral given below.
$$ \int_{-\infty}^{+\infty} \exp{\left(-\frac{(x - \mu)^2}{2\sigma^2}\right)} \text{erf}\left(\alpha \frac{x-\mu}{\sqrt{2}\sigma}\...

-2
votes

1
answer

167
views

### Simple closed form for $\int \lfloor x \rfloor dx$? [closed]

Wolfram Alpha claims there is no closed form in terms of standard funcions
for $\int \lfloor x \rfloor dx$ but we believe we found
simple closed form agreeing with experimental data.
Define $i_1(x)=x -...

7
votes

2
answers

404
views

### A method to generate solvable equations of degrees $p = 7, 13, 19, 31, 37,\dots$ using only cubics

I've always wondered if the DeMoivre method to generate an algebraic number $x_p$,
$$x_p = u_1^{1/p}+u_2^{1/p}$$
of degree $p$ using only quadratic roots $u_i$ could be generalized using cubic roots $...

0
votes

0
answers

27
views

### Distribution of the second bigger value among m Gaussian draws

$\DeclareMathOperator\erf{erf}$
Let's consider the set $\Omega_m$ of $m$ i.i.d. Gaussian variables $\{X_1, X_2, \dots, X_m \}$, with $X_i \sim \mathcal{N} \left( 0, \sigma^2 \right) \forall i$.
$\...

2
votes

0
answers

154
views

### Closed form for the A347205

Let $q(n)$ be A007814, i.e., number of trailing zeros in the binary representation of $n$. Here
$$q(2n+1)=0, q(2n)=q(n)+1$$
Let $\operatorname{wt}(n)$ be A000120, i.e., number of $1$'s in binary ...

2
votes

0
answers

111
views

### Closed form for the sum of the integer coefficients

Let $a(n)$ be A002720, i.e., number of partial permutations of an $n$-set; number of $n \times n$ binary matrices with at most one $1$ in each row and column.
$$a(n)=\sum\limits_{k=0}^{n} k!\binom{n}{...

4
votes

2
answers

778
views

### Integral of a product between two normal distributions and a monomial

The integral of the product of two normal distribution densities can be exactly solved, as shown here for example.
I'm interested in compute the following integral (for a generic $n \in \mathbb{N}$):
$...

3
votes

1
answer

106
views

### Convolution between normal distribution and the maximum over $m$ Gaussian draws

$\DeclareMathOperator\erf{erf}$
Let's consider the Gaussian distribution $P_X(x)= \frac{1}{\sqrt{2 \pi \sigma^2}} e^{- \frac{x^2}{2 \sigma^2}}$. Now consider the random variable $W \equiv \max \{ X_1, ...

2
votes

0
answers

68
views

### Closed form for the number of permutations with a given excedance set

Let $q(n)$ be A007814, i.e., number of trailing zeros in the binary representation of $n$. Here
$$q(2n+1)=0, q(2n)=q(n)+1$$
Let $\operatorname{wt}(n)$ be A000120, i.e., number of $1$'s in binary ...

0
votes

0
answers

92
views

### Closed form for the number of steps required to get $n$ balls in the last box

Let $\operatorname{wt}(n)$ be A000120, i.e., number of $1$'s in binary expansion of $n$ (or the binary weight of $n$).
Then we have an integer sequence given by
$$a(n)=n(n+1)-\sum\limits_{k=0}^{n}\...

0
votes

0
answers

22
views

### Families of 1st order recursive relations with closed forms

A general 1st order recurrence relation can be expressed as $X_{n+1} = f(X_{n},n)$.
I am looking for a source, list of functions or statement about $f$ such that an $F$ exists which expresses $X_{n} = ...

0
votes

0
answers

64
views

### Examples of $f(n,m)$-solvable recurrences

Let $a_k(n)$ be an integer sequence given by recurrence relation
$$a_k(2n+1)=a_k(n), a_k(2n)=a_k(n)+\sum\limits_{j=1}^{i}a_k(g_j(n)), a_k(0)=1$$
Here $g_j(n)$ are some functions in most cases based on ...

2
votes

0
answers

56
views

### any ideas on how to solve matrix equation like this $X A_i Y = B_i$

the objective function is like
$$\operatorname*{argmin}_{X,Y} = \sum_i \|X A_i Y - B_i\|_F^2$$, and $A_i$ is a diagonal matrix
I've tried gradient-descent, but as it turns out not well, I wonder if ...

2
votes

0
answers

115
views

### Closed form for coefficients related to excedance set of permutation

Working on suitable closed form for A329369, I discovered very useful coefficients, which have the following recurrence relation:
$$T(0,1)=T(0,2)=1$$
$$T(n,1)=1, n>0$$
$$T(0,k)=0, k>2$$
$$T(2n+1,...

3
votes

0
answers

159
views

### Closed form for $a(2^m(2^n-2^p-1))$

Let $q(n)$ be A007814, i.e., the number of trailing zeros in the binary representation of $n$. Here
$$q(2n+1)=0, q(2n)=q(n)+1$$
Let $a(n)$ be A329369. Here
$$a(2n+1)=a(n), a(2n)=a(n)+a(n-2^{q(n)})+a(...

4
votes

1
answer

180
views

### Closed-form examples of CMC surfaces

Besides the trivial cases of cylinders and spheres, are there any other known examples of non-zero constant mean curvature surfaces which can be represented explicitly in a closed form? I am ...

1
vote

1
answer

105
views

### Number of steps required to get one ball in each box for $n=2^k$

Given $n$ balls, all of which are initially in the first of $n$ numbered boxes, $a(n)$ is the number of steps required to get one ball in each box when a step consists of moving to the next box every ...

3
votes

1
answer

497
views

### Is there real or complex analytic function whose positive real zeros are the primes?

Related to this question
Q1 Is there real or complex analytic function $f(x)$ such
that its positive real zeros are the primes and it is
given in closed form of compositions of already named ...

9
votes

1
answer

728
views

### Closed form for ₄F₃(n,n,n,2n;1+n,1+n,1+n;−1)

For positive integer $n$ the following value of a hypergeometric function
$$_4F_3(n,n,n,2n,1+n,1+n,1+n,-1)$$
based on the first few terms looks like
$$ R_1(n) + R_2(n) \pi^2$$
where $R_{1,2}(n)$ are ...

1
vote

0
answers

164
views

### Solution that minimizes the sum of squared errors, with quadratic constraints

Given symmetric and positive definite $n \times n$ (real) matrices $A_1, \dots, A_m$ and $b_1, \dots, b_m \in {\Bbb R}^{n}$, I am trying to find the solution with the least sum of squared errors of ...

2
votes

0
answers

64
views

### How to extend this sum involving generalized harmonic numbers?

It is well-known since Euler that the Generalized harmonic numbers, defined for $n\in\mathbb N$ by $$H_n^{(r)}=\sum_{k=1}^n\frac1{k^r},$$ can be naturally extended for non integer $n$ in terms of ...

2
votes

1
answer

143
views

### How to solve for $a$ in $\sum_{j=i}^n (a -j) \binom{n}{j} y^j (1-y)^{n-j} = 0$

The Problem
Given $i, n, y$, I am trying to find a closed form solution for $a$ in the equation
$$
\sum_{j=i}^n (a -j) \binom{n}{j} y^j (1-y)^{n-j}
=
0
$$
Do you have any recommendations on how to ...

1
vote

1
answer

296
views

### Is this long closed form for pi trivial?

With the help of wolfram alpha we got very long closed form
for $\pi$ in terms of algebraic numbers, logarithms of algebraic
numbers and $cot^{-1},coth^{-1}$ which can be expressed as logarithms.
From ...

9
votes

3
answers

508
views

### Why mpmath computes $\sum_{n=2}^\infty (-1)^n\log(n)=\log\left(\frac1 2 \sqrt{2} \sqrt{\pi}\right)$

Working with precision 500 decimal digits, mpmath in sage computes:
$$\sum_{n=2}^\infty (-1)^n\log(n)=\log\left(\frac1 2 \sqrt{2} \sqrt{\pi}\right).\tag{1}\label{1}$$
We believe the LHS of \eqref{1} ...

4
votes

3
answers

1k
views

### Surprisingly long closed form for simple series

For natural $A$ define
$$ f(A)=\sum_{n=1}^\infty \frac{1}{A^n}\left(\frac{1}{An+1}- \frac{1}{An+A-1}\right)$$
$f(A)$ is BBP (Bailey-Borwein-Plouffe) formula and allows digit extraction in base $A$.
...