Take the tour ×  I am teaching a combinatorics class in which I
introduced the notion of a "mass formula". My terminology is
inspired by the Smith–Minkowski–Siegel mass formula for the
total mass of positive-definite quadratic forms of a given size
and genus. That famous mass formula is much too fancy of an
example for my class. All that I really do is define the concept
of the "mass" of a combinatorial object to be $1/|G|$ if $G$ is
its automorphism group, and then argue that it can be easier to
find the total mass of a collection of objects than to count
them straight (using Polya counting theory). For example, the
total mass of unlabeled trees of order $n$ is $n^{n-2}/n!$,
because there are $n^{n-2}$ labeled trees.  So I have two
questions for which a quick answer (i.e. sooner than two weeks)
would be most convenient:    1. Is "mass formula" a standard
name for this concept? Is there a standard name?   2. Can
someone suggest a free on-line reference, comparable to a
Wikipedia page or a little longer? The c