All Questions
25 questions
26
votes
2
answers
1k
views
Partitions to different parts not exceeding $n$
Consider the polynomial $(1+x)(1+x^2)\dots (1+x^n)=1+x+\dots+x^{n(n+1)/2}$, which enumerates subj. How to prove that it's coefficients increase up to $x^{n(n+1)/4}$ (and hence decrease after this)? Or ...
- 109k
17
votes
1
answer
756
views
Congruences Ramanujan-style
Let $t\in\Bbb{N}$ and consider the sequences $p_t(n)$ defined by
$$\sum_{n\geq0}p_t(n)x^n=\prod_{i\geq1}\frac1{(1-x^i)^t}=(x;x)_{\infty}^{-t}.$$
The numbers $p_t(n)$ can be regarded as enumerating ...
- 43.2k
15
votes
0
answers
767
views
Wherefore art thou a Borcherds Product?
This question essentially asks how can one recognize (or rule out) that a generating function of combinatorial origin may be given as a Borcherds type product. I'll start with a motivational example: ...
- 85.6k
12
votes
2
answers
716
views
Alternating sum of hook lengths: Part I
Given $\lambda$ an integer partition of $n$, let $h_{ij}(\lambda)$ denote the hook length of cell $(i,j)$ in the Young diagram of $\lambda$.
Is there a closed formula or a generating function for the ...
- 43.2k
10
votes
1
answer
625
views
Generating function for A261041
Let $a(n)$ be A261041 (i.e., number of partitions of subsets of $\{1,2,\dotsc,n\}$, where consecutive integers are required to be in different parts).
Let $b(n)$ be an integer sequence with generating ...
- 4,938
10
votes
1
answer
207
views
Generating function for A225114
Let $a(n)$ be A225114 (i.e., number of skew partitions of $n$ whose diagrams have no empty rows and columns).
Let $b(n)$ be an integer sequence with generating function $B(x)$ such that
$$
B(x) = \...
- 4,938
8
votes
2
answers
4k
views
What are the best known bounds on the number of partitions of $n$ into exactly $k$ distinct parts?
For example, if $n = 10$ and $k = 3$, then the legal partitions are
$$10 = 7 + 2 + 1 = 6 + 3 + 1 = 5 + 4 + 1 = 5 + 3 + 2$$
so the answer is $4$. By choosing $k$ random elements of $\{1,\ldots,2n/k\}$, ...
- 195
8
votes
1
answer
368
views
generalizing Wilf's conjecture: Uppuluri-Carpenter numbers
The complementary Bell numbers have the exponential generating function
$$\sum_{n\geq0}\tilde{B}_nx^n=e^{1-e^x}.$$
Herb Wilf conjectured that $\tilde{B}_n=0$ only for $n=2$. By now, there are a few ...
- 43.2k
5
votes
1
answer
223
views
Coefficients obtained from ratio with partition number generating function
This is a question inspired by T. Amdeberhan's recent question, as well as another previos MO question.
For an integer partition $\lambda$, and $k\in \mathbb{N}\cup\{\infty\}$, let $|\lambda|_k$ ...
- 24.2k
5
votes
1
answer
361
views
Does the ordinary generating function of Bell numbers converge?
I am working in a field not really based on combinatorics, therefore I appologize if my question is in any kind invalid. Nevertheless, in my calculations, the Bell numbers appeared. I need to find ...
- 51
5
votes
1
answer
204
views
Collapsed partitions and generating functions
Given $n\in\Bbb{N}$, the number of (unrestricted) integer partitions of $n$ are given by
$$\sum_{n\geq0}p(n)x^n=\prod_{j\geq1}\frac1{1-x^j}.$$
Define the collapsed partitions of $n$ to be the ...
- 43.2k
5
votes
1
answer
289
views
The number of partitions between two fixed partitions
Given two partitions M and N, with $M_i \leq N_i$ for all $1\leq i\leq \max\{l(M),l(N)\}$. Is there a formula for the generating function: $$\sum_{\lambda: M_i\leq \lambda_i\leq N_i} q^{|\lambda|}$$...
- 499
5
votes
0
answers
105
views
Hooks, monomers, dimers and Young diagrams: Part II
As promised, I've upgraded my last question.
Consider the $k$-by-$n$ partition $\lambda_n=(n,\dots,n)$ and its corresponding Young diagram $Y_{n,k}$, which is a $k\times n$ rectangle of cells. Now, ...
- 43.2k
4
votes
0
answers
211
views
Sum $f(n_1,n_2,\ldots,n_k) 1^{n_1} 2^{n_2} \ldots k^{n_k}$ over partitions
Use the notation $(n_1,n_2,\ldots,n_k) \vdash n$ to denote that $(n_1,n_2,\ldots,n_k)$ is a partition of the positive integer $n$, that is, $n_1+n_2+\ldots+n_k = n$ and $n_1 \ge n_2 \ge \ldots \ge n_k ...
- 261
4
votes
0
answers
154
views
Hooks, monomers, dimers and Young diagrams: Part I
Following Richard Stanley's pointers regarding my earlier MO question, I decided to "scale-down" the problem and add a slight "twist" to it.
Consider the one-line partition $\lambda_n=(n)$ and its ...
- 43.2k
3
votes
1
answer
272
views
Generating function for parity in hooks
Let $\lambda\vdash n$ denote an integer partition of $n$ and $\frak{H}_{\lambda}$ be the multiset of hook lengths of $\lambda$. Further, let $o(\lambda)=\#$ of odd entries and $e(\lambda)=\#$ of even ...
- 43.2k
3
votes
1
answer
621
views
Recurrence relation for coefficients of product of generating functions for partition numbers
It is well known that
$$Z(x,q) = \prod_{n=1}^\infty\frac{1}{(1-xq^n)} = \sum_{m=0}^\infty\sum_{k=0}^m p_{m,k}x^kq^m$$
is the generating function for the number $p_{m,k}$ of partitions of $m$ in ...
- 81
3
votes
0
answers
222
views
Number of partitions of set restricted by sum of square of part size
Let $p_1^{a_1}p_2^{a_2}\cdots$ denotes the integer partition of $n$, i.e. $a_1p_1+a_2p_2+\cdots=n$. Or equivalently $m_1+m_2+\cdots=n$. It is known that the number of partitions of set $\{x_1,x_2,\...
- 405
3
votes
0
answers
123
views
$q$-series for the number of rectangles in a square lattice
Given a partition $\lambda\vdash n$ of $n$, look at its Young diagram $Y_{\lambda}$. Let $a(\lambda)$ be the number of squares (of all sizes) in $Y_{\lambda}$. For example, if $n=4$ then $a(4)=4, a(3,...
- 43.2k
3
votes
0
answers
312
views
Enumerating a class of polynomials
How many equivalence classes of $\Bbb F_2[x,y]$ polynomials with $x$ degree $n_x$ and $y$ degree $n_y$ are there such that each $y^i$ coefficient (polynomial in $\Bbb Z[x]$) is distinct and $x^i$ ...
user76479
2
votes
1
answer
400
views
An infinite product: combinatorial interpretation
It is an undergraduate exercise to show that the generating function for the sequence of unrestricted integer partitions $p(n)$ is the celebrated infinite product
$$\prod_{k=1}^{\infty}\frac{1}{1-x^k}...
- 1,561
2
votes
1
answer
160
views
An inequality on partitions into distinct bounded parts
Let $P(n,m)$ denote the set of all positive integer partitions of $n$ into parts that are pairwise distinct and bounded by $m$. Let $p(n,m) = |P(n,m)|$.
After some numerical experiments it appears
$...
- 305
1
vote
1
answer
235
views
partition theory: meet the COP
Recall that $(a;q)_0:=1,\,(a;q)_n=(1-a)(1-aq)(1-aq^2)\cdots(1-aq^{n-1})$ and
$(a;q)_{\infty}=(1-a)(1-aq)(1-aq^2)\cdots$. Let's introduce the following (generalized) concept.
A colored overpartition (...
- 43.2k
1
vote
1
answer
270
views
Integer partitions with subset sums "not divisible" by p
I have the following questions: Let $N \in \mathbb{N}$ and
\begin{equation}
\sum_{i=1}^k n_i = N,
\end{equation}
with $n_i \in \mathbb{N}$ for $1 \le i \le k$ and some $k \in \mathbb{N}$, be an ...
- 101
1
vote
0
answers
164
views
How to prove this identity? (Perhaps related to partition) [closed]
How to prove this identity?
$ \sum_{n\ge 0} \frac{x^{n^2}}{(1-x)(1-x^2)\cdots(1-x^n)}= \frac{1}{\prod_{k \ge 0}(1-x^{5k+1})(1-x^{5k+4})}$
I will appreciate it a lot if a solution using method ...
- 281