We characterize the power series ${\sum }_{n=0}^{\infty }{c}_n{z}^n$ with the geometric property that, for sufficiently many points $z$, $\left|z\right|=1$, a circle $C\left(z\right)$ contains infinitely many partial sums. We show that ${\sum }_{n=0}^{\infty }{c}_n{z}^n$ is a rational function of special type; more precisely, there are $t\in ℝ$ and $n_0$, such that, the sequence $c_n{e}^{\mathrm{int}}$, $n\ge n_0$, is periodic. This result answers in the affirmative a question of J.-P. Kahane and furnishes stronger versions of the main results of [Katsoprinakis, Arkiv for Matematik]. We are led to consider special families of circles $C\left(z\right)$ with...

We present a new method of analytic continuation of series out of their disk of convergence. We then exhibit a connection with the phenomenon of bifurcation delay in a planar discrete dynamical system; the limit of the method is then related to a stop phenomenon.

Soient $P\left(\underset{\_}{x}\right)=P(x_1,...,x_n)$ et $Q\left(\underset{\_}{x}\right)=Q(x_1,...,x_n)$ deux polynômes à coefficients positifs vérifiant :$$\underset{\genfrac{}{}{0pt}{}{\left|\underset{\_}{x}\right|\to +\infty }{x_1,...,x_n\ge 1}}{lim}\frac{P\left(\underset{\_}{x}\right)}{Q\left(\underset{\_}{x}\right)}=+\infty .$$Soient $\underset{\_}{\eta }=({\eta }_1,...,{\eta }_n)\in {\mathbf{N}}^n$ et $R=P/Q$. On étudie la série de Dirichlet $Z(R,\underset{\_}{\eta };s)={\sum }_{{\eta }_1,...,{\eta }_n=1}^{\infty }{\underset{\_}{\eta }}^{\underset{\_}{\eta }}R(\underset{\_}{\eta }{)}^{-s}$ : abscisse de convergence absolue, existence et nature du prolongement méromorphe, ordre de grandeur dans les bandes verticales. On donne un procédé de construction du prolongement méromorphe de la fonction $s\mapsto Z(R,\underset{\_}{\eta };s)$ qui ne dépend que de $\underset{\_}{\eta }$ et de certains monômes de $P$ et $Q$: les monômes extrémaux.