  We solve, analytically and numerically, a gap equation in parity invariant
QED_3 in the presence of an infrared cutoff \mu and derive an expression for
the critical fermion number N_c as a function of \mu. We argue that this
dependence of N_c on the infrared scale might solve the discrepancy between
continuum Schwinger-Dyson equations studies and lattice simulations of QED_3.
