  The Hodge series of a finite matrix group is the generating function for
invariant exterior forms of specified order and degree. Lauret, Miatello, and
Rossetti gave examples of pairs of non-conjugate cyclic groups having the same
Hodge series; the corresponding space forms are isospectral for the Laplacian
on p-forms for all p, but not for all natural operators. Here we explain,
simplify, and extend their investigations
