Questions tagged [integer-sequences]
For questions about sequences of integers. References are often made to the online resource oeis.org.
265
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Why are these Littlewood-Richardson coefficients congruent to 1 mod 8?
Let $n\in{\mathbb N}$ and write $n=q_1+q_2+\dots+q_t$, where $q_1>q_2>\dots>q_t$ are powers of $2$. Let $\lambda_n$ be the partition with Frobenius symbol $(q_1-1,q_2-1,\dots,q_t-1;q_t,q_{t-1}...
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2
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1
answer
97
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Conjectural congruences for numbers related to Littlewood-Richardson coefficients
For $n \geq 0$, let $a_n$ be the square of the Euclidean length of the vector of Littlewood-Richardson coefficients of $\sum_{\lambda \vdash n} s_\lambda^2$, where $s_\lambda$ are the symmetric Schur ...
- 17.2k
6
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0
answers
122
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Do you recognize these numbers related to the higher Airy equations?
I'm studying the higher Airy equations
$$\left[\big({-}\tfrac{\partial}{\partial y}\big)^{n-1} - y\right] \psi = 0$$
under a coordinate transformation. The interesting coefficients $c_n^{(1)}, \ldots, ...
- 2,159
2
votes
1
answer
123
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Difference sequences of sets of integers
In this paper, the conception of the difference sequence and $\infty$-difference length of a subset of groups is introduced. As an important case, subsets of the additive group of integers are ...
- 977
1
vote
0
answers
79
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A definition related to pseudoprimes and the Dedekind psi function
In this post we consider that $\psi(k)$ denotes the Dedekind psi function. Wikipedia has an artcle dedicated to this arithmetic function Dedekind psi function defined for a positive integers $m>1$ ...
- 37
0
votes
1
answer
73
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Reducing recurrence relations mod10 [closed]
I have been playing around with integer sequences as of late, and the following question occurred to me:
Suppose for $m$ fixed we have some some initial values $a_1,\cdots,a_m$ and for all $n\in\...
1
vote
1
answer
162
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Invariants ("checksums", "hash") for collection of integers
The sum of a collection of integers doesn't depend on the order of the integers and can detect the corruption of one element of the collection (but multiple elements can get corrupted without their ...
- 159
20
votes
2
answers
552
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What is the smallest size of a shape in which all fixed $n$-polyominos can fit?
Let $n$ be an integer and consider all fixed $n$-polyominos, i.e., without rotation or reflection. I am interested in finding a shape in which all polyominos can embed. (It is OK if multiple ...
- 369
5
votes
1
answer
265
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Combinatorics related plane geometry
There are $n$ men, standing one at each vertex of a convex $n$-gon. If they are allowed to move together along sides or diagonals of the polygon to reach another vertex, how many different ways are ...
- 103
3
votes
1
answer
124
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Limit associated with two Beatty sequences that are not a Beatty pair
Suppose that $r>1$ and $s>1$ are irrational numbers, and let $a_n=\lfloor nr \rfloor$ and $b_n=\lfloor ns \rfloor$. Assume that $r$ and $s$ are numbers for which $\{a_n\}\cap\{b_n\}$ is ...
- 391
3
votes
1
answer
182
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Numbers $n$ whose representation as the product of two divisors require more digits than that of $n$
Note: Posting in MO since it was unanswered in MSE
Let $f(x)$ be the number of digits in the decimal representation of $x$ e.g. $, f(0) = 1, f(1729) = 4$. If $n = ab$ then we can show that $f(ab) > ...
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5
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0
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525
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A generalization of the difference of two squares identity
This question deals with finding explicit integer functions for the coefficients of the monomial expansion of the polynomial
$$
Q \left( x_1, \ldots , x_n \right) = \prod_{\kappa_1, \ldots , \kappa_{n-...
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6
votes
1
answer
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Sequence A76132 eventually periodic modulo $2,3$ and $5$
Sequence A76132 starting as $1,1,2,4,10,36,218,\ldots$ of the OEIS is recursively defined by $a(1)=1$
and $a(n)=\sum_{k=1}^{n-1}a(n-k)^k$ for $n\geq 2$.
It is eventually periodic of period 1,1 and 34 ...
- 13.6k
5
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1
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A common combinatorial description for a certain type of recurrences
For integer-valued sequences $(x_n)_{n=0}^\infty$, consider recurrences of the form
$$x_n=ax_{n-1}+(bn+c)x_{n-2} \tag{$*$}\label{star}$$
for $n\ge2$, where $a,b,c$ are integers.
There seem to be many ...
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3
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2
votes
0
answers
98
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How to compute/estimate the least $k$ such that there exist $n$ consecutive integers each having a prime factor $\le k$?
Let $a_n$ be the least integer $k$ such that there exist $n$ consecutive integers each with a prime factor $\le k$. For example, $a_{13} \le 11$ because the 13 consecutive integers $114,115,\ldots,126$...
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1
vote
1
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Polynomials, $3^x$ and the Collatz conjecture
$\DeclareMathOperator\Orb{Orb}\newcommand\abs[1]{\lvert#1\rvert}$The Collatz or the $3n+1$ conjecture is open.
Are there non-trivial polynomials $f(x)\in\mathbb Z[x]$ and $g(x)\in\mathbb R[x]$ having ...
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6
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0
answers
623
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Is Collatz conjecture known to be true for specific numbers?
The Collatz or the $3n+1$ conjecture is open.
Is there a specific polynomial $f(x)\in\mathbb Z[x]$ whose range is unbounded for which every integer of form $|f(m)|$ at $m\in\mathbb Z$ satisfies $3n+1$...
- 12.8k
-2
votes
1
answer
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Why do we need to represent integers as the sum of three cubes? [closed]
It is conjectured that for any integer $k\not\equiv \pm 4\pmod 9$ there are infinitely many integer solutions to
$$
a^3+b^3+c^3=k.
$$
Some cases for integer $k$ becomes too hard like $42$ which it ...
- 2,123
3
votes
2
answers
138
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Limit of the Schröder numbers ratio
I have been playing around with interesting integer sequences and came across Schröder number which defines the number of lattice paths of n x n grid.
The recurrence formula to calculate these numbers ...
21
votes
1
answer
2k
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Reference request: a tale of two mathematicians
I've heard tell the following anecdote involving Pierre Gabriel and Jacques Tit at least twice in a lapse of four years or so:
When P. Gabriel presented the theorem in a conference [sometime around ...
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4
votes
0
answers
323
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The largest digital sum of the square of an n-digit number
The sequence $13, 31, 46, 63, 81, 97, 112, 130, 148, 162, 180, \dots,$ (sequence A348300 in the OEIS) shows the largest digital sum the square of an $n$-digit (decimal) number has.
Is this sequence ...
- 3,229
4
votes
1
answer
149
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Why do convoluted convolved Fibonacci numbers pop up from this triangle?
Start with this triangle (OEIS A118981). This triangle is simple to generate with the following recurrence relation (though $T(0,0)$ ends up different from the OEIS version):
$$
T(0,0) = 2;T(1,0) = 1;...
- 153
2
votes
1
answer
119
views
On gaps in a sequence of integers
Given a fixed $p \in \{3,4,5,\ldots\}$, we define the strictly increasing sequence $\{a_k\}_{k\in \mathbb N}$ as follows. We set $a_{p,1}=1$ and for each $k>1$, we set $a_{p,k}$ to be the least ...
- 2,858
4
votes
1
answer
139
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Integer sequences with unique $k$-subsets sum
let the $\binom{\mathfrak{M}}{k}$ be a shorthand notation for chosing $k$ elements of set $\mathfrak{M}$ of positive integers and let $\left|\binom{\mathfrak{M}}{k}\right|$ denote the sum of the ...
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3
votes
1
answer
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Tangent numbers, secant numbers and permanent of matrices
Inspired by Question 402572, I consider the permanent of matrices
$$f(n)=\mathrm{per}(A)=\mathrm{per}\left[\operatorname{sgn} \left(\sin\pi\frac{j+2k}{n+1} \right)\right]_{1\le j,k\le n},$$
where $n$ ...
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0
votes
1
answer
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Where is the source of the formula $\sum_{j=0}^\infty \bigl(j+\frac{1}{2}\bigr)^{n-1}\frac{2^{j+1/2}}{\binom{2j+1}{j+1/2}}$ for an integer sequence?
The infinite series representation
\begin{equation}
\frac1\pi\sum_{j=0}^\infty \biggl(j+\frac{1}{2}\biggr)^{n-1}\frac{2^{j+1/2}}{\binom{2j+1}{j+1/2}}, \quad n\ge0
\end{equation}
for the positive ...
- 390
8
votes
1
answer
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Possible small mistake in Bilu-Hanrot-Voutier paper on primitive divisors of Lehmer sequences (?)
I think that I might have spotted I small mistake (a missing $5$-defective Lehmer pair) in the classification of terms of Lehmer sequences without primitive divisors given in:
1 Bilu, Hanrot, and ...
- 55
0
votes
1
answer
418
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New experiments involving Ramanujan primes: Benford's law
I know that in the literature there are interesting articles involving the sequence of Ramanujan primes, I refer the Ramanujan Prime from the online encyclopedia Wolfram MathWorld. This week I ...
- 37
6
votes
5
answers
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Bounds for $a(n)=a(n-1)+a(\lfloor n/2 \rfloor)$
This is related to problem in graph theory.
OEIS defines A033485 as
$a(1)=1$ and $a(n)=a(n-1)+a(\lfloor n/2 \rfloor)$.
Q1 what are upper bounds and asymptotics for $a(n)$, can we get $\exp(o(n))$?
...
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1
vote
1
answer
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Bounds for the sequence $a(n,A)=n*a(\lfloor (1-A)n \rfloor,A)$
Related to this question and possibly the open problem
of the exponential time hypotheses.
Let $A$ be rational number, $0 < A < 1$.
For positive integer $n$, define the sequence
$a(1,A)=1$ and $(...
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0
votes
0
answers
57
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Reference request: Counting integer sequences in homogeneous linear recurrences
Are there references in the literature that deal with the probability of finding an integer sequence in a linear homogeneous recurrence with constant coefficients $ \in \mathbb{Z}$? (or provides a way ...
14
votes
4
answers
2k
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Integrality of a sequence formed by sums
Consider the following sequence defined as a sum
$$a_n=\sum_{k=0}^{n-1}\frac{3^{3n-3k-1}\,(7k+8)\,(3k+1)!}{2^{2n-2k}\,k!\,(2k+3)!}.$$
QUESTION. For $n\geq1$, is the sequence of rational numbers $a_n$ ...
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5
votes
1
answer
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Upper bound an integral with exponential function
I am working on my research about approximation a function. I come up with the following integral. I run some simulations and saw that the integral would converge to zero as n goes to infinty. Here is ...
- 95
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votes
0
answers
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Does $a_{i}(n)$ hit every positive integers infinitely many times for all $i\ge1$?
This question is related to a family of sequences. I have a simple definition as below and I have a question based on my limited observations for $i\le200$ and $n \le 10^{9}$.
Definition. $a_{i}(1) = ...
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3
votes
1
answer
84
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Avoiding equality of partial sums of two different aperiodic sequences
Consider two distinct sequences of positive integers, $a_{n}|_{n=1}^{\infty}$, and $b_{n}|_{n=1}^{\infty}$ such that for either sequence no period exists. The elements of both sequences are drawn from ...
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2
votes
1
answer
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Euler quotients modulo $n$
For odd integer $n$, define the Euler quotient modulo $n$ to be $a(n)$:
$$ a(n)=\frac{(2^{\phi(n)}-1) \bmod n^2}{n}=\frac{2^{\phi(n)}-1}{n} \bmod n$$
$a(n)=0$ for OEIS sequence Wieferich numbers
...
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5
votes
1
answer
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In the Oldenburger-Kolakoski sequence, is #1s = #2s infinitely many times?
The Oldenburger-Kolakoski sequence, $OK$, is the unique sequence of $1$s and $2$s that starts with $1$ and is its own runlength sequence:
$$OK = (1,2,2,1,1,2,1,2,2,1,2,2,1,1,2,1,1,2,2,1,2,1,1,\ldots).$...
- 391
3
votes
1
answer
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The sequence $a(n)=(2^n \bmod p)^{p-1} \bmod p^2$
Related to this question.
Let $p$ be prime and $n$ positive integer.
Define $a(n)=(2^n \bmod p)^{p-1} \bmod p^2$
Let $D(n)$ be the base $2$ discrete logarithm of $a(n)$, i.e.
given $p,a(n)$ we have $2^...
- 23.3k
5
votes
1
answer
250
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Discrete logarithm and the sequence $a(n)=(g^n \bmod p)^{p-1} \bmod p^2$
Let $p$ be prime and $g,n$ integers.
Define $a(n)=(g^n \bmod p)^{p-1} \bmod p^2$
By mod p we don't mean congruence, but the reduction modulo $p$ operator. $A \bmod ...
- 23.3k
1
vote
1
answer
217
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Sequences over finite fields
Let's we have finite field $F_q$ for some prime $q=2^M-1$.
I am looking for special sequence {$a_{i}$, $i \in {1,..,q-1}$},
($\{a_{1},...,a_{q-1}\}=F_q/\{0\}$) with the following properties:
$r_{1}=...
- 33
2
votes
2
answers
262
views
sum of odious numbers to the power of k
In number theory, an odious number is a positive integer that has an odd number of $1$s in its binary expansion.
The first odious numbers are:
$1, 2, 4, 7, 8, 11, 13, 14, 16, 19, 21, 22, 25, 26, 28, ...
- 29
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votes
0
answers
282
views
Convergence of rivers of numbers
$\DeclareMathOperator{\river}{river}\DeclareMathOperator{\leadingsum}{ls}\DeclareMathOperator{\digitsum}{ds}\newcommand{\qed}{\square}
$A 1999 British Informatics Olympiad question asks about ...
- 119
6
votes
0
answers
124
views
Upper bounds for a sequence of integers
Given $\alpha\geq0$ we consider the sequence
$$
C_k=k^\alpha\sum_{j=0}^{k-1}C_jC_{k-1-j}
$$
with $C_0=1$. I'm interested in upper bounds (in terms of $\alpha$) for such a sequence. I know that when $\...
- 813
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votes
0
answers
117
views
Writing integers as sequences of products by 2 and integer divisions by 3
For any integer, we consider its decompositions into sequences of products by $2$ and integer division by $3$.
For instance:
$$
100 = 2 \cdot 2 \cdot 2 \cdot 2 \cdot 2 \cdot 2 \cdot 2 \cdot 2 \cdot 2 \...
- 1,255
12
votes
1
answer
365
views
Subwords of the infinite Fibonacci word
Let $W = 01001010010010 \ldots$ be the infinite Fibonacci word, A003849 in the OEIS. Let $B(m)$ be the set of $m+1$ subwords of $W$ that have length $m$, and for each such subword $u$, let $p(u)$ be ...
- 391
5
votes
1
answer
174
views
Is this Laurent phenomenon explained by invariance/periodicity?
In Chapter 4 of his Tracking the Automatic
Ant, David Gale
discusses three families of recursively defined sequences of numbers, all
due to Dana Scott and inspired by the Somos sequences:
Sequence 1. ...
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3
votes
1
answer
271
views
Why does this "factorial sequence" appear in the OEIS?
For a reciprocal of a polynomial, $f = \frac{1}{p}$, we (presumably) may construct a sequence $(c_n)_{n=0}^\infty$ such that for all $N\ge 0$
$$f(k)k! = \sum_{n=0}^{N-1} c_n(k-n)! + O((k-N)!). $$
I ...
- 935
32
votes
0
answers
2k
views
The easily bored sequence
If we want to compare the repetitiveness of two finite words, it looks reasonable, first of all, to consider more repetitive the word repeating more times one of its factors, and secondarily to ...
- 3,053
17
votes
2
answers
908
views
A conjecture harmonic numbers
I will outlay a few observations applying to the harmonic numbers that may be interesting to prove (if it hasn't already been proven).
From the Online Encyclopedia of Positive Integers we have:
$a(n)$ ...
- 171