We consider an N=1 U(N) gauge theory with matter in the antisymmetric
representation and its conjugate, with a tree level superpotential containing
at least quartic interactions for these fields. We obtain the effective
glueball superpotential in the classically unbroken case, and show that it has
a non-trivial N-dependence which does not factorize. We also recover additional
contributions starting at order S^N from the dynamics of Sp(0) factors. This
can also be understood by a precise map of this theory to an Sp(2N-2) gauge
theory with antisymmetric matter.Comment: 22 pages. v2: comment (and a reference) added at the end of section 2
on low rank cases; minor typos corrected. v3: 2 footnotes added with
additional clarifications; version to appear in journa