scholarly journals Kolakoski sequence: links between recurrence, symmetry and limit density

2021 ◽  
Vol 4 (1) ◽  
pp. 29-44
Author(s):  
Alessandro Della Corte ◽  
Keyword(s):  
Sufficient Conditions ◽  
Asymptotic Density ◽  
Unique Element ◽  
Run Length ◽  
Open Questions ◽  
Mirror Reversal ◽  
Reversal Invariance

The Kolakoski sequence $S$ is the unique element of \(\left\lbrace 1,2 \right\rbrace^{\omega}\) starting with 1 and coinciding with its own run length encoding. We use the parity of the lengths of particular subclasses of initial words of \(S\) as a unifying tool to address the links between the main open questions - recurrence, mirror/reversal invariance and asymptotic density of digits. In particular we prove that recurrence implies reversal invariance, and give sufficient conditions which would imply that the density of 1s is \(\frac{1}{2}\).

scholarly journals On powerful numbers

1986 ◽  
Vol 9 (4) ◽  
pp. 801-806 ◽  
Author(s):  
R. A. Mollin ◽  
P. G. Walsh
Keyword(s):  
Positive Integer ◽  
Sufficient Conditions ◽  
Necessary And Sufficient Conditions ◽  
Effective Algorithm ◽  
Existence Proof ◽  
Prime Decomposition ◽  
Open Questions ◽  
Necessary And Sufficient ◽  
Powerful Numbers

A powerful number is a positive integernsatisfying the property thatp2dividesnwhenever the primepdividesn; i.e., in the canonical prime decomposition ofn, no prime appears with exponent 1. In [1], S.W. Golomb introduced and studied such numbers. In particular, he asked whether(25,27)is the only pair of consecutive odd powerful numbers. This question was settled in [2] by W.A. Sentance who gave necessary and sufficient conditions for the existence of such pairs. The first result of this paper is to provide a generalization of Sentance's result by giving necessary and sufficient conditions for the existence of pairs of powerful numbers spaced evenly apart. This result leads us naturally to consider integers which are representable as a proper difference of two powerful numbers, i.e.n=p1−p2wherep1andp2are powerful numbers with g.c.d.(p1,p2)=1. Golomb (op.cit.) conjectured that6is not a proper difference of two powerful numbers, and that there are infinitely many numbers which cannot be represented as a proper difference of two powerful numbers. The antithesis of this conjecture was proved by W.L. McDaniel [3] who verified that every non-zero integer is in fact a proper difference of two powerful numbers in infinitely many ways. McDaniel's proof is essentially an existence proof. The second result of this paper is a simpler proof of McDaniel's result as well as an effective algorithm (in the proof) for explicitly determining infinitely many such representations. However, in both our proof and McDaniel's proof one of the powerful numbers is almost always a perfect square (namely one is always a perfect square whenn≢2(mod4)). We provide in §2 a proof that all even integers are representable in infinitely many ways as a proper nonsquare difference; i.e., proper difference of two powerful numbers neither of which is a perfect square. This, in conjunction with the odd case in [4], shows that every integer is representable in infinitely many ways as a proper nonsquare difference. Moreover, in §2 we present some miscellaneous results and conclude with a discussion of some open questions.

Invertible and regular completions of operator matrices

2015 ◽  
Vol 30 ◽  
pp. 530-549 ◽  
Author(s):  
Dragana Cvetkovic-Ilic
Keyword(s):  
Sufficient Conditions ◽  
Operator Matrix ◽  
Operator Matrices ◽  
Open Questions ◽  
Regular Operators

In this paper, for given operators A ∈ B(X) and B ∈ B(Y), the set of all C ∈ B(Y,X) such that the operator matrix M_C = \left[ \begin{array}{cc} A & C \\ O & B \end{array} \right] is injective, invertible, left invertible and right invertible, is described. Answers to some open questions are given. Also, in the case when A and B are relatively regular operators, the set of all C ∈ B(Y,X) such that M_C is regular is described. In addition, a necessary and a sufficient conditions are given for MC to be regular with the inner inverse of a certain given form.

On the Set of Common Differences in van der Waerden’s Theorem on Arithmetic Progressions

1999 ◽  
Vol 42 (1) ◽  
pp. 25-36 ◽  
Author(s):  
Tom C. Brown ◽  
Ronald L. Graham ◽  
Bruce M. Landman
Keyword(s):  
Positive Integer ◽  
Arithmetic Progression ◽  
Infinite Number ◽  
Necessary Conditions ◽  
Sufficient Conditions ◽  
Arithmetic Progressions ◽  
Large Set ◽  
Open Questions ◽  
The Family ◽  
Positive Integers

AbstractAnalogues of van derWaerden’s theorem on arithmetic progressions are considered where the family of all arithmetic progressions, AP, is replaced by some subfamily of AP. Specifically, we want to know for which sets A, of positive integers, the following statement holds: for all positive integers r and k, there exists a positive integer n = w′(k, r) such that for every r-coloring of [1, n] there exists a monochromatic k-term arithmetic progression whose common difference belongs to A. We will call any subset of the positive integers that has the above property large. A set having this property for a specific fixed r will be called r-large. We give some necessary conditions for a set to be large, including the fact that every large set must contain an infinite number of multiples of each positive integer. Also, no large set {an : n = 1, 2,…} can have . Sufficient conditions for a set to be large are also given. We show that any set containing n-cubes for arbitrarily large n, is a large set. Results involving the connection between the notions of “large” and “2-large” are given. Several open questions and a conjecture are presented.

scholarly journals Subdominant positive solutions of the discrete equationΔu(k+n)=−p(k)u(k)

2004 ◽  
Vol 2004 (6) ◽  
pp. 461-470 ◽  
Author(s):  
Jaromír Baštinec ◽  
Josef Diblík
Keyword(s):  
Positive Solution ◽  
Positive Solutions ◽  
Sufficient Conditions ◽  
Discrete Equation ◽  
Positive Coefficient ◽  
Open Questions ◽  
Existence Of Positive Solutions

A delayed discrete equationΔu(k+n)=−p(k)u(k)with positive coefficientpis considered. Sufficient conditions with respect topare formulated in order to guarantee the existence of positive solutions ifk→∞. As a tool of the proof of corresponding result, the method described in the author's previous papers is used. Except for the fact of the existence of positive solutions, their upper estimation is given. The analysis shows that every positive solution of the indicated family of positive solutions tends to zero (ifk→∞) with the speednot smaller than the speed characterized by the functionk·(n/(n+1))k. A comparison with the known results is given and some open questions are discussed.

NECESSARY AND SUFFICIENT CONDITIONS FOR FREQUENT CAUCHY SEQUENCES

2009 ◽  
Vol 02 (02) ◽  
pp. 295-305
Author(s):  
Chuan Jun Tian ◽  
Sui Sun Cheng ◽  
Mehmet Gürdal
Keyword(s):  
Necessary Conditions ◽  
Sufficient Conditions ◽  
Necessary And Sufficient Conditions ◽  
Asymptotic Density ◽  
Frequency Measure ◽  
Cauchy Sequences ◽  
Natural Density ◽  
Sufficient And Necessary Conditions ◽  
Necessary And Sufficient

In this paper, by means of frequency measure (also called asymptotic density or natural density) defined for integer subsets, we obtain some new explicit sufficient and necessary conditions for real sequences to be frequently convergent. These conditions involve frequent Cauchy sequences and statistical pre-Cauchy sequences as well as statistical Cauchy sequences.

Some Contributions to the Theory of Near-Critical Bisexual Branching Processes

2007 ◽  
Vol 44 (02) ◽  
pp. 492-505
Author(s):  
M. Molina ◽  
M. Mota ◽  
A. Ramos
Keyword(s):  
Branching Process ◽  
Branching Processes ◽  
Sufficient Conditions ◽  
Positive Probability ◽  
Limit Laws ◽  
Bisexual Branching Processes ◽  
Probabilistic Evolution

We investigate the probabilistic evolution of a near-critical bisexual branching process with mating depending on the number of couples in the population. We determine sufficient conditions which guarantee either the almost sure extinction of such a process or its survival with positive probability. We also establish some limiting results concerning the sequences of couples, females, and males, suitably normalized. In particular, gamma, normal, and degenerate distributions are proved to be limit laws. The results also hold for bisexual Bienaymé–Galton–Watson processes, and can be adapted to other classes of near-critical bisexual branching processes.

The extinction time of a general birth and death process with catastrophes

1986 ◽  
Vol 23 (04) ◽  
pp. 851-858 ◽  
Author(s):  
P. J. Brockwell
Keyword(s):  
Laplace Transform ◽  
Size Distribution ◽  
Sufficient Conditions ◽  
Necessary And Sufficient Conditions ◽  
Death Process ◽  
Extinction Time ◽  
Birth And Death Process ◽  
Different Types ◽  
The Laplace Transform ◽  
Necessary And Sufficient

The Laplace transform of the extinction time is determined for a general birth and death process with arbitrary catastrophe rate and catastrophe size distribution. It is assumed only that the birth rates satisfyλ0= 0,λj> 0 for eachj> 0, and. Necessary and sufficient conditions for certain extinction of the population are derived. The results are applied to the linear birth and death process (λj=jλ, µj=jμ) with catastrophes of several different types.

Normal approximations to discrete unimodal distributions

1986 ◽  
Vol 23 (04) ◽  
pp. 1013-1018
Author(s):  
B. G. Quinn ◽  
H. L. MacGillivray
Keyword(s):  
Stationary Distribution ◽  
Sufficient Conditions ◽  
Random Variables ◽  
Hypergeometric Distribution ◽  
Death Process ◽  
Normal Approximations ◽  
Discrete Random Variables ◽  
Birth Death

Sufficient conditions are presented for the limiting normality of sequences of discrete random variables possessing unimodal distributions. The conditions are applied to obtain normal approximations directly for the hypergeometric distribution and the stationary distribution of a special birth-death process.

What’s Next?

2011 ◽  
Vol 23 (1) ◽  
pp. 60-63 ◽  
Author(s):  
Peter Vorderer
Keyword(s):  
Cultural Differences ◽  
Factor Model ◽  
New Developments ◽  
Theoretical Concepts ◽  
Open Questions ◽  
Entertainment Products ◽  
Entertainment Theory

This paper points to new developments in the context of entertainment theory. Starting from a background of well-established theories that have been proposed and elaborated mainly by Zillmann and his collaborators since the 1980s, a new two-factor model of entertainment is introduced. This model encompasses “enjoyment” and “appreciation” as two independent factors. In addition, several open questions regarding cultural differences in humans’ responses to entertainment products or the usefulness of various theoretical concepts like “presence,” “identification,” or “transportation” are also discussed. Finally, the question of why media users are seeking entertainment is brought to the forefront, and a possibly relevant need such as the “search for meaningfulness” is mentioned as a possible major candidate for such an explanation.

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