Volumes of spheres and special values of zeta functions of $\mathbb{Z}$ and $\mathbb{Z}\mathrm{/}n\mathbb{Z}$

The volume of the unit sphere in every dimension is given a new interpretation as a product of special values of the zeta function of $\mathbb{Z}$, akin to volume formulas of Minkowski and Siegel in the theory of arithmetic groups. A product formula is found for this zeta function that specializes to Catalan numbers. Moreover, certain closed-form expressions for various other zeta values are deduced, in particular leading to an alternative perspective on Euler’s values of the Riemann zeta function.