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1. CMB 2011 (vol 56 pp. 251)

Borwein, Peter; Choi, Stephen K. K.; Ganguli, Himadri
 Sign Changes of the Liouville Function on Quadratics Let $\lambda (n)$ denote the Liouville function. Complementary to the prime number theorem, Chowla conjectured that \begin{equation*} \label{a.1} \sum_{n\le x} \lambda (f(n)) =o(x)\tag{$*$} \end{equation*} for any polynomial $f(x)$ with integer coefficients which is not of form $bg(x)^2$. When $f(x)=x$, $(*)$ is equivalent to the prime number theorem. Chowla's conjecture has been proved for linear functions, but for degree greater than 1, the conjecture seems to be extremely hard and remains wide open. One can consider a weaker form of Chowla's conjecture. Conjecture 1. [Cassaigne et al.] If $f(x) \in \mathbb{Z} [x]$ and is not in the form of $bg^2(x)$ for some $g(x)\in \mathbb{Z}[x]$, then $\lambda (f(n))$ changes sign infinitely often. Clearly, Chowla's conjecture implies Conjecture 1. Although weaker, Conjecture 1 is still wide open for polynomials of degree $\gt 1$. In this article, we study Conjecture 1 for quadratic polynomials. One of our main theorems is the following. Theorem 1 Let $f(x) = ax^2+bx +c$ with $a\gt 0$ and $l$ be a positive integer such that $al$ is not a perfect square. If the equation $f(n)=lm^2$ has one solution $(n_0,m_0) \in \mathbb{Z}^2$, then it has infinitely many positive solutions $(n,m) \in \mathbb{N}^2$. As a direct consequence of Theorem 1, we prove the following. Theorem 2 Let $f(x)=ax^2+bx+c$ with $a \in \mathbb{N}$ and $b,c \in \mathbb{Z}$. Let $A_0=\Bigl[\frac{|b|+(|D|+1)/2}{2a}\Bigr]+1.$ Then either the binary sequence $\{ \lambda (f(n)) \}_{n=A_0}^\infty$ is a constant sequence or it changes sign infinitely often. Some partial results of Conjecture 1 for quadratic polynomials are also proved using Theorem 1. Keywords:Liouville function, Chowla's conjecture, prime number theorem, binary sequences, changes sign infinitely often, quadratic polynomials, Pell equationCategories:11N60, 11B83, 11D09

2. CMB 2011 (vol 55 pp. 774)

Mollin, R. A.; Srinivasan, A.
 Pell Equations: Non-Principal Lagrange Criteria and Central Norms We provide a criterion for the central norm to be any value in the simple continued fraction expansion of $\sqrt{D}$ for any non-square integer $D>1$. We also provide a simple criterion for the solvability of the Pell equation $x^2-Dy^2=-1$ in terms of congruence conditions modulo $D$. Keywords:Pell's equation, continued fractions, central normsCategories:11D09, 11A55, 11R11, 11R29

3. CMB 2009 (vol 52 pp. 63)

Dietmann, Rainer
 Small Zeros of Quadratic Forms Avoiding a Finite Number of Prescribed Hyperplanes We prove a new upper bound for the smallest zero $\mathbf{x}$ of a quadratic form over a number field with the additional restriction that $\mathbf{x}$ does not lie in a finite number of $m$ prescribed hyperplanes. Our bound is polynomial in the height of the quadratic form, with an exponent depending only on the number of variables but not on $m$. Categories:11D09, 11E12, 11H46, 11H55

4. CMB 2007 (vol 50 pp. 191)

Drungilas, Paulius; Dubickas, Artūras
 Every Real Algebraic Integer Is a Difference of Two Mahler Measures We prove that every real algebraic integer $\alpha$ is expressible by a difference of two Mahler measures of integer polynomials. Moreover, these polynomials can be chosen in such a way that they both have the same degree as that of $\alpha$, say $d$, one of these two polynomials is irreducible and another has an irreducible factor of degree $d$, so that $\alpha=M(P)-bM(Q)$ with irreducible polynomials $P, Q\in \mathbb Z[X]$ of degree $d$ and a positive integer $b$. Finally, if $d \leqslant 3$, then one can take $b=1$. Keywords:Mahler measures, Pisot numbers, Pell equation, $abc$-conjectureCategories:11R04, 11R06, 11R09, 11R33, 11D09

5. CMB 2006 (vol 49 pp. 481)

Browkin, J.; Brzeziński, J.
 On Sequences of Squares with Constant Second Differences The aim of this paper is to study sequences of integers for which the second differences between their squares are constant. We show that there are infinitely many nontrivial monotone sextuples having this property and discuss some related problems. Keywords:sequence of squares, second difference, elliptic curveCategories:11B83, 11Y85, 11D09

6. CMB 2005 (vol 48 pp. 121)

Mollin, R. A.
 Necessary and Sufficient Conditions for the Central Norm to Equal $2^h$ in the Simple Continued Fraction Expansion of $\sqrt{2^hc}$ for Any Odd $c>1$ We look at the simple continued fraction expansion of $\sqrt{D}$ for any $D=2^hc$ where $c>1$ is odd with a goal of determining necessary and sufficient conditions for the central norm (as determined by the infrastructure of the underlying real quadratic order therein) to be $2^h$. At the end of the paper, we also address the case where $D=c$ is odd and the central norm of $\sqrt{D}$ is equal to $2$. Keywords:quadratic Diophantine equations, simple continued fractions,, norms of ideals, infrastructure of real quadratic fieldsCategories:11A55, 11D09, 11R11

7. CMB 2002 (vol 45 pp. 428)

Mollin, R. A.
 Criteria for Simultaneous Solutions of $X^2 - DY^2 = c$ and $x^2 - Dy^2 = -c$ The purpose of this article is to provide criteria for the simultaneous solvability of the Diophantine equations $X^2 - DY^2 = c$ and $x^2 - Dy^2 = -c$ when $c \in \mathbb{Z}$, and $D \in \mathbb{N}$ is not a perfect square. This continues work in \cite{me}--\cite{alfnme}. Keywords:continued fractions, Diophantine equations, fundamental units, simultaneous solutionsCategories:11A55, 11R11, 11D09

8. CMB 2000 (vol 43 pp. 218)

Mollin, R. A.; van der Poorten, A. J.
 Continued Fractions, Jacobi Symbols, and Quadratic Diophantine Equations The results herein continue observations on norm form equations and continued fractions begun and continued in the works \cite{chows}--\cite{mol}, and \cite{mvdpw}--\cite{schinz}. Categories:11R11, 11D09, 11R29, 11R65