For a radioactive material, its activity A and rate of change of its activity R are defined as $$A = - \frac{dN}{dt}$$ and $$R = - \frac{dA}{dt},$$ where N(t) is the number of nuclei at time t. Two radioactive sources P (mean life $$\tau$$) and Q (mean life $$2\tau$$) have the same activity at t = 0. Their rates of change of activities at $$t = 2\tau$$ are $$R_P$$ and $$R_Q$$, respectively. If $$\frac{R_P}{R_Q} = \frac{n}{e},$$ then the value of n is