The propose of this paper
is to define numerical invariants of odd-dimensional surgery obstructions,
computable in a way similar to that used to compute the index and Arf
invariants of even-dimensional surgery obstructions. The main result is that a
system of integral congruences (“numerical invariants”) suffices, modulo the
projective class group, to determine whether or not an odd-dimensional
surgery obstruction vanishes, when the fundamental group is a finite 2-group.
In addition, the numerical invariants turn out to be Euler characteristics
in certain cases of topological interest, including the existence of product
formulas.