Approximation numbers of composition operators on the $H^2$ space of Dirichlet series

Hervé Queffélec, Kristian Seip

By a theorem of Gordon and Hedenmalm, $\phi$ generates a bounded composition operator on the Hilbert space ${\mathcal{H}}^2$ of Dirichlet series ${\sum }_n{b}_n{n}^{-s}$ with square-summable…