  We consider a mixture of two single-spin-state fermions with an interaction
of negligible range and infinite $s$-wave scattering length. By varying the
mass ratio $\alpha$ across $\alpha_c\simeq 13.6069$ one can switch on-and-off
the Efimov effect. We determine analytically the third cluster coefficient of
the gas. We show that it is a smooth function of $\alpha$ across $\alpha_c$
since, unexpectedly, the three-body parameter characterizing the interaction is
relevant even on the non-Efimovian side $\alpha<\alpha_c$.
