The question is very simple: 

Find a prime divisor of $\frac{(10^{13}-1)}{9}$ , i.e. $11\cdots11$($13$ ones), also known as [$R^{(10)}\_{13}$ or $R\_{13}$](http://en.wikipedia.org/wiki/Repunit). Same question for $R\_{79}$.

Of course, calculating the answer using a calculator is simple, but I have no idea how to tackle it.
Furthermore, we know by Fermatss little theorem that $10^{12}=1 \pmod{13}$, but I can't seem to apply this to this problem.
Thanks in advance.