All Questions
66 questions
1
vote
0
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114
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Generalized identity with Stirling numbers of the second kind and falling factorials
It is known that Striling numbers of the second kind satisfy the relation
$$
\sum\limits_{k=0}^{n}{n \brace k}(x)_k = x^n.
$$
where $(x)_n$ is the falling factorials such that
$$
(x)_n = x(x-1)(x-2)\...
- 4,928
0
votes
1
answer
169
views
Partial sums of binomial coefficients and related family of polynomials
Let $a(n)$ be A302117. Here
$$
a(n) = 4(n-1)a(n-1) - \frac{1}{3}\prod\limits_{k=0}^{n-1}(2k-3), \\
a(0) = 0.
$$
Let
$$
T(n,k) = \sum\limits_{i=0}^{k} \binom{n}{i}.
$$
Let $P_n(z)$ be the family of ...
- 4,928
3
votes
1
answer
192
views
Density of Pisot polynomials
Recall that a Pisot polynomial $P=x^n+ a_{n-1}x^{n-1}\ldots a_1$ has integer coefficients, a real root $x_1>1$ and all other roots $|x_i|<1$ for $1\leq i \leq n$. One key result is that $\{(...
- 680
2
votes
0
answers
113
views
Numbers of positive terms in polynomials equal A069999
Let $a(n)$ be A069999 (i.e., number of possible dimensions for commutators of $n \times n$ matrices; it is independent of the field). OEIS states that no generating function is known.
Let $P(n,k)$ be ...
- 4,928
0
votes
0
answers
60
views
Algorithm for $q$-Bell numbers
Let $T(n,k)$ be A126347 (i.e., triangle, read by rows, with row polynomials $B(n, q)$). Here
$$
B(n, q) = \sum\limits_{k=0}^{n-1}\binom{n-1}{k}B(k, q)q^k, \\
B(0, q) = 1.
$$
Start with vector $\nu$ of ...
- 4,928
7
votes
0
answers
208
views
How biased is $(x_i x_j)_{i,j}$, $x_i\in \mathbb{F}_2$?
Let $N = \frac{n (n-1)}{2}$. Let $V$ be the $N$-dimensional vector space over $\mathbb{F}_2$ consisting of tuples $(x_{(i,j)})_{1\leq i <j \leq n}$, $x_{(i,j)}\in \mathbb{F}_2$. Let $S$ be the set ...
- 20.2k
3
votes
0
answers
213
views
A family of polynomials related to integer partitions
For a positive integer $n$, let $p(n)$ be the number of partitions of $n$.
For $1\le k\le n$, let $p(n,k)$ denote the number of partitions of $n$ having exactly $k$ terms; in other words, $p(n,k)$ is ...
- 15.6k
0
votes
0
answers
121
views
Closed form of coefficients of a finite field polynomial
I want to find a valid polynomial for a finite field $\mathbb{Z}_p[x]_{f(x)}$ with $d=deg(f(x))$. For this definition to hold, it can be deduced that $p$ must be prime and the polynomial $f(x)$ ...
- 47
2
votes
1
answer
310
views
Generating function for A300483 (related to Chebyshev polynomial of first kind)
Let $a(n)$ be A300483. Here
$$
a(n) = 2\int\limits_{t \geqslant 0}T_n\left(\frac{t+1}{2}\right)\exp(-t)\,dt.
$$
where $T_n(x)$ is $n$-th Chebyshev polynomial of first kind.
Let $b(n)$ be an integer ...
- 4,928
2
votes
0
answers
70
views
Property of a family of simple polynomials related to the A329369
Let $a(n)$ be A329369 (i.e., number of permutations of $\{1,2,\dotsc,m\}$ with excedance set constructed by taking $m-i$ ($0 < i < m$) if $b(i-1) = 1$ where $b(k)b(k-1)\cdots b(1)b(0)$ ($0 \...
- 4,928
2
votes
1
answer
372
views
On properties of sums involving the floor function
During my research on properties of fractional part and integer part functions, I was led to consider the function of two variables $f(n,k)=\frac{2^{k}+1}{2^{ n}+1}\left\lfloor \frac{2^{n}+1}{2^{k}+1}\...
- 611
3
votes
0
answers
240
views
On thickness of binary polynomials
OEIS A169945 introduces the concept of thickness of a polynomial as the magnitude of the largest coefficient in the expansion of the square of the polynomial. Considering the $2^{n+1}$ polynomials $p(...
- 791
17
votes
1
answer
687
views
Multiply an integer polynomial with another integer polynomial to get a "big" coefficient
I have copied this question from StackExchange, in the hope that some experts here can provide some relevant insight. Thanks to Greg Martin for improving the question.
Given $f(x) = a_0 + a_1 x + a_2 ...
- 823
4
votes
0
answers
263
views
Cosine Modulo $p$?
Consider the integers modulo a prime $p$. I'm looking for a nice polynomial function that acts as a sort of "cosine" on the integers modulo $p$. Specifically, I'm looking for solutions to ...
- 591
1
vote
0
answers
69
views
Simplification of computing $f(n,z)$
Let
$$
s(n,z)=\sum\limits_{j=0}^{n}L(n,j,z)
$$
where
$$
L(n,j,z)=\sum\limits_{p=0}^{n-j-1}f(p,z)L(n-j-1,p,z), \\
L(n,n,z)=1
$$
Now let $s(n,z)$ be an arbitrary function such that $s(0, z)=1$. It means ...
- 4,928
1
vote
0
answers
180
views
Applications of hyperbolic polynomials?
The recently posted MO-Q "Positivity of the coefficients of Taylor series associated to the Riemann hypothesis" (see also this MO-Q) has re-kindled my interest in hyperbolic polynomials--...
- 10.5k
3
votes
2
answers
459
views
Short sequence beats long sequence
I have encountered some comparison between two binomial sums. It was amusing how the one with "fewer" summands exceeds (in value) than the other which consists of many more terms. In fact, ...
- 43.2k
3
votes
1
answer
210
views
Powers of $2$ up to $2^{m-1}$ from a polynomial of degree $m-1$
Let $T(n,k)$ be a triangle of coefficients such that $T(n,k)\geqslant0$ for $n>0$, $0<k\leqslant n$, $0$ otherwise. Also
$$T(2n+1,1)=\frac{1}{2n+1}, T(2n,1)=0$$
$$T(n,k)=\frac{1}{n}(T(n-1,k-1)+(...
- 4,928
5
votes
1
answer
358
views
The number of polynomials on a finite group, II
This question is follow up of this MO-post.
First let us recall the necessary definitions.
A function $f:X\to X$ on a group $X$ is called a polynomial if there exists $n\in\mathbb N$ and elements $a_0,...
- 41.8k
3
votes
1
answer
194
views
Checking presence of a specific term in product polynomial
I have a multivariate polynomial $P$ which is a product of $M$ low degree polynomials $p_i$
$$P(x_1, x_2, \dotsc, x_n) = \prod_{i=1}^M p_i(x_1, x_2, \dotsc, x_n)$$
where the maximum degree of each $...
- 103
3
votes
0
answers
144
views
Flat polynomials with factors of big height
Let $p(x)$ be a polynomial of degree $n$ with all coefficients in $\{-1,0,1\}$ (such polynomials are sometimes called flat). I am wondering how big the coefficients of a factor of $p$ can be. Call ...
- 13.4k
4
votes
0
answers
186
views
A problem in the spirit of P. Borwein's polynomials
A well-known conjecture (now a theorem) of P. Borwein (see Wang and Krattenthaler - An asymptotic approach to Borwein-type sign pattern theorems) states:
For all positive integers $n$, the sign ...
- 43.2k
1
vote
0
answers
159
views
A follow up on Bergeron's conjecture and a question
We say two polynomials satisfy $P(x)\geq Q(x)$ iff $P(x)-Q(x)$ has non-negative coefficients. Recall $(n)_q!=\prod_{j=1}^n(1-q^j)$ and the Gaussian polynomials $\binom{n}k_q=\frac{(n)_q!}{(k)_q!(n-k)...
- 43.2k
4
votes
1
answer
539
views
A (mild?) question on the number of monomials
Let $[n]_q=\frac{1-q^n}{1-q}$ with $[0]_q=0$. Recall the $q$-factorials $[n]_q!=[1]_q[2]_q\cdots[n]_q$ (with $[0]_q!=1$) and the $q$-binomials
$$\binom{n}k_q=\frac{[n]_q!}{[k]_q!\,[n-k]_q!}.$$
Now, ...
- 43.2k
2
votes
1
answer
213
views
Coefficient of a term in a several variable polynomial multipled with Vandermonde determinant
Let $\Delta_n(x_1, \ldots, x_n)$ denote the Vandermonde determinant $\displaystyle \prod_{1 \leq i < j \leq n}(x_j - x_i)$. Let $c_1, \ldots, c_n$ and $K$ be nonnegative integers satisfying
$$c_1 + ...
- 167
2
votes
1
answer
385
views
Determinants of striped Hankel matrices
This question is related to the matrices described in Deyi Chen's recent MO post (look at some examples there). The main difference: we are asking for a determinant evaluation instead of a permanent, ...
- 43.2k
6
votes
1
answer
242
views
$(q,t)$-Fibonacci polynomials: area & bounce statistics
This is related to my earlier (unanswered) MO post. Preserve notations from there.
We take advantage of the one-to-one correspondence between the $(s,s+1)$-core partitions and $(s,s+1)$-Dyck paths. ...
- 43.2k
3
votes
1
answer
372
views
How many ways can $N$ be written as a sum of terms in the form $2^i3^j$?
Given a positive integer $N$, let $f(N)$ be the number of ways $N$ can be decomposed as a sum of terms of the form $2^i3^j$, where each such term appears at most once in the sum. For example, $f(10) = ...
- 1,703
1
vote
0
answers
96
views
Polynomial composition utilizing polynomials in two different finite fields
At every $n\in\mathbb N$ (all polynomials are of degree $O(1)$) is there $g_{3,1}^{(n)},\dots,g_{3,k}^{(n)}\in\mathbb F_3[x_1,\dots,x_n]$ at $k=\mathsf{poly}(n)$ and $g_2^{(n)}\in\mathbb F_2[x_1,\dots,...
- 13.9k
1
vote
0
answers
107
views
Palindromicity of $q$-polynomials related to Catalan triangles
The present problem comes from further consideration of my earlier questions, from here and here.
Start with the following variants of Catalan triangles
$\frac{2k+1}{n+k+1}\binom{2n}{n-k}$. Now, ...
- 43.2k
3
votes
0
answers
195
views
Congruence for the polynomials $(t+1)^n$
An interesting polynomial congruence is given by
$$A_n(t^m)\equiv \left(\frac{1+t+\cdots+t^{m-1}}m\right)^{n+1}A_n(t) \qquad \mod (t-1)^{n+1}, \tag1$$
where $A_n(t)$ are the Eulerian polynomials with ...
- 43.2k
11
votes
1
answer
332
views
Counting monomials in product polynomials: Part II
Encouraged by the responses to my earlier MO question, here is a follow up and upgraded quest.
Let $e\geq2$ be an integer. Define the polynomials
$$P_{n,e}(x)=\prod_{i=1}^{n-1}\left(1+x^{e^{i-1}}+x^{e^...
- 43.2k
9
votes
2
answers
538
views
Counting monomials in product polynomials: Part I
This question is motivated by recent work of R P Stanley, Theorems and conjectures on some rational generating functions. Consider the polynomials
$$P_n(x)=\prod_{i=1}^{n-1}(1+x^{3^{i-1}}+x^{3^i}).$$
...
- 43.2k
9
votes
1
answer
1k
views
"Laurent phenomenon"?
Define the recurrence
\begin{align*}
n(2n+x-3)u_n(x)
&=2(2n+x-2)(4n^2+4nx-8n-3x+3)u_{n-1}(x) \\
&-4(n+x-2)(2n-3)(2n+2x-3)(2n+x-1)u_{n-2}(x)
\end{align*}
with initial conditions $u_0(x)=0$ and $...
- 43.2k
1
vote
1
answer
241
views
Integral zeros of a multivariate polynomial
Consider the multivariate polynomial
$$f(x_1,\ldots,x_m)=mk\sum_{i=1}^mx_i^2-mk(k-1)\sum_{i=1}^mx_i-\left(\sum_{i=1}^mx_i\right)^2,$$
for integers $m,k\ge2$. We are looking for integral zeros of $f$ ...
- 33
3
votes
0
answers
243
views
Interlacing sequences by polynomials?
Given $t=2^\ell$ where $\ell\in\mathbb N_{>0}$ and $M\in\mathbb Z$ and two sets of integers $\{a_1,\dots,a_t\}$ and $\{b_1,\dots,b_t\}$ with $0<a_1\leq \dots\leq a_t<M$ and $0<b_1\leq \...
- 13.9k
17
votes
2
answers
1k
views
$P(x)=P(y)$ has infinitely many integer solutions
Determine all polynomials $P(x)$ with integer coefficients such that $P(x)=P(y)$ has infinitely many integer solutions in integer $x$ and $y$ with $x \neq y$.
Choose $P(x)=a_n(x-k)^{2n}+a_{n-1}(x-k)^{...
- 501
17
votes
1
answer
500
views
Irreducibility of root-height generating polynomial
The height $ht(\alpha)$ of a positive root $\alpha$ in a (finite, crystallographic) root system $\Phi$ is $\sum_{i=1}^n c_i$ where $\alpha = \sum_{i=1}^n c_i \alpha_i$ is its decomposition as a sum of ...
- 2,753
2
votes
1
answer
192
views
A Vandermonde-type system
For a prime $p$ and $a_1,\dotsc,a_n\in\mathbb F_p^\times$, consider the system of equations
$$ \begin{cases}
\begin{align}
a_1 + \dotsb + a_n &= 0 \\
a_1x_1 + \dotsb + a_nx_n &...
- 23k
4
votes
1
answer
139
views
Polynomial expansions via prime-base digits
Fix a prime number $p$. If $n$ is a positive integer, then denote
$$\text{$\omega_{p,k}(n):=\#$ of $k$'s in the $p$-ary expansion of $n$}$$
and the total sum of all its $p$-ary digits by
$$\Omega_p(...
- 43.2k
1
vote
1
answer
552
views
Coefficients $U_m(n,k)$ in the identity $n^{2m+1}=\sum\limits_{0\leq k \leq m}(-1)^{m-k}U_m(n,k)\cdot n^k$
Review the main result of mathoverflow.net/questions/297900, that is the identity
\begin{equation}\label{f1}
n^{2m+1}=\sum\limits_{1\leq k \leq n}\sum\limits_{j\geq0}A_{m,j}k^j(n-k)^j,
\end{equation}
...
- 167
11
votes
0
answers
450
views
A congruence involving roots of unity
Let $f(x) \in \mathbb{Z}[x]$ and suppose $f(\omega^j) \in \mathbb{Z}$ for all $j= 1, \dots, n$ where $\omega = e^{2 \pi i/n}$ is a primitive $n^{\text{th}}$ root of unity.
Computational evidence ...
- 305
8
votes
2
answers
565
views
integral transform of Fibonacci polynomials is integral
The Fibonacci polynomials are defined recursively by $F_0(x)=0, F_1(x)=1$ and $F_n(x)=xF_{n-1}(x)+F_{n-2}(x)$, for $n\geq2$.
While computing certain integrals, I observe the following (numerically) ...
- 43.2k
7
votes
3
answers
735
views
Expanding in Fibonacci powers
Let $F_n$ denote the all-familiar Fibonacci numbers, with $F_0=0, F_1=1, F_2=1$, etc.
There is a plethora of properties for these numbers involving their sums, products, convolutions and so on. Here, ...
- 43.2k
9
votes
1
answer
285
views
Multivariate quasipolynomials and where to find them
This question is inspired from thinking about David Speyer's question about complex variable Ehrhart theory.
In one variable, Ehrhart theory has been vastly generalized. For example it has been ...
- 85.6k
3
votes
3
answers
233
views
sequencial shift on families =flipped powers. How?
Consider the following family of functions
$$f_n(w):=\sum_{k=0}^{\infty}\frac{(-1)^{k-1}}{k!}(k+n)^{k-1}w^k.$$
QUESTION 1. Does the following hold?
$$f_n(w)=-\frac1{n(f_{-1}(w))^n}.$$
Deeper ...
- 43.2k
5
votes
1
answer
211
views
degree of a polynomial over set-partitions
Denote $(x)_t = x(x-1)(x-2)\cdots(x-t+1)$ and fix some $t_1,\dots,t_n\in\mathbb{N}$. Now consider the polynomials
$$f_n(x)=\sum_{\pi\in L[n]}(-1)^{\vert\pi\vert-1}(\vert\pi\vert-1)!\prod_{A\in\pi}(x)_{...
- 43.2k
7
votes
1
answer
232
views
counting monomials and integrality
For $n\in\mathbb{Z}^{+}$, consider the polynomials
$$P_n(x)=\prod_{k=0}^{n-1}(x^n-x^k).$$
QUESTION. Is it possible to find a closed formula for the number of monomials in $P_n(x)$, after expansion?
...
- 43.2k
16
votes
2
answers
1k
views
are these polynomials or rationals functions?
Let $x$ be a variable. Define the following family of sequences (reminiscent of Lucas polynomials) according to the rule: $P_0(x):=0, P_1(x):=1$ and for $n\geq2$ by
$$P_n(x)=xP_{n-1}(x)-P_{n-2}(x).$$
...
- 43.2k
9
votes
2
answers
546
views
Can you tie up these Laurent sequences?
Fix an integer $k\geq3$. Define the two families of sequences $\{x_n\}$ and $\{y_n\}$ according to the rules:
$$x_n=\frac{x_{n-1}^2+x_{n-2}^2+\cdots+x_{n-k+1}^2}{x_{n-k}} \qquad n\geq k$$
and
$$y_n=\...
- 43.2k