The Cauchy transform of a measure in the plane, $$ F(z) = \frac{1}{2\pi i}\int_{\C} \frac{1}{z-w} \,d\mu(w)\hbox{,} $$ is a useful tool for numerical studies of the measure, since the measure of any reasonable set may be obtained as the line integral of $F$ around the boundary. We give an effective algorithm for computing $F$ when $\mu$ is a self-similar measure, based on a Laurent expansion of $F$ for large $z$ and a transformation law (Theorem 2.2) for $F$ that encodes the self-similarity of $\mu$. Using this algorithm we compute $F$ for the normalized Hausdorff measure on the Sierpiński gasket. Based on this experimental evidence, we formulate three conjectures concerning the mapping properties of $F$, which is a continuous function holomorphic on each component of the complement of the gasket.

Non-positively curved triangles of finite groups are of cohomological dimension 2 over the rationals and have Property FA. We classify triangles of finite groups which satisfy certain geometric conditions including the Gauss--Bonnet theorem. We investigate whether or not these groups are virtually torsion-free, contain a free abelian subgroup of rank 2, are residually finite or are linear.

Periodic configurations, or oscillators, occur in many cellular automata. In an oscillator, repeated applications of the automaton rules eventually restore the configuration to its initial state. This paper considers oscillators in Conway's Life; analogous techniques should apply to other rules. Three explicit methods are presented to construct oscillators in Life while guaranteeing certain complexity bounds, leading to the existence of \begin{itemize} \item an infinite sequence $K_n$ of oscillators of periods $n=58$, 59, 60, \dots \ and uniformly bounded population, and \item an infinite sequence $D_n$ of oscillators of periods $n=58$, 59, 60, \dots \ and diameter bounded by $b \sqrt{\log n}$, where $b$ is a uniform constant. \end{itemize} The proofs make use of the first explicit example of a stable glider reflector in Life, solving a longstanding open question about this cellular automaton.

We determine the solutions in integers of the equation $ y^2 = ( x + p ) ( x^2 + p^2 ) $ for $ p = 167$, $223$, $337$, $1201$. The method used was suggested to us by Yu. Bilu, and is shown to be in some cases more efficient than other general purpose methods for solving such equations, namely the elliptic logarithms method and the use of Thue equations.

We give upper bounds on the size of the gap between the constant term and the next nonzero Fourier coefficient of an entire modular form of given weight for $\flop{L}{-.3}\!_0(2)$. Numerical evidence indicates that a sharper bound holds for the weights $h \equiv 2 \pmod 4$. We derive upper bounds for the minimum positive integer represented by level-two even positive-definite quadratic forms. Our data suggest that, for certain meromorphic modular forms and $p=2$, $3$, the $p$-order of the constant term is related to the base-$p$ expansion of the order of the pole at infinity.

This paper examines the question of whether there is an unbounded walk of bounded step size along Gaussian primes. Percolation theory predicts that for a low enough density of random Gaussian integers no walk exists, which suggests that no such walk exists along prime numbers, since they have arbitrarily small density over large enough regions. In analogy with the Cramér conjecture, I construct a random model of Gaussian primes and show that an unbounded walk of step size $k@\sqrt{\log |z|}$ at $z$ exists with probability 1 if $k\More \sqrt{2\ppi\lmbda_c}$, and does not exist with probability 1 if $k \Less \sqrt{2\ppi\lmbda_c}$, where $\lmbda_c\Approx 0$.$35$ is a constant in continuum percolation, and so conjecture that the critical step size for Gaussian primes is also $\sqrt{2\ppi\lmbda_c\log|z|}$.