Poisson summation formulas involving the sum-of-squares function

We obtain new Poisson type summation formulas with nodes ±n\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \pm \sqrt n $$\end{document} and with weights involving the function rk(n) that gives the number of representations of a positive integer n as the sum of k squares. Our results extend summation formulas due to Guinand and Meyer that involve the sum-of-three-squares function r3(n).