Recently A. Terras established
some (soon to be published) relations between the values of Riemann’s zeta function
at consecutive positive integral argument and values of certain modified
Bessel functions. By combining these relations with some previous results
concerning the values of ζ(s) at odd, positive integers (Grosswald-Nachrichten
Akad. Wiss. Göttingen, II Math.-Phys. Klasse 1970, pp. 9–13) it follows that
certain infinite series of exponentials and divisor functions (somewhat reminiscent of
Lambert series) are rational valued.