induction - For every natural number $n$, $3^{3n} - 1$ is divisible by $26$.

Use induction to prove that for every natural number $n$, $3^{3n} - 1$ is divisible by $26$.

I can see that for $n=1$, $3^{3} -1=26\cdot 1$. As for inductive step, assuming that the statement holds for $n=k$ ($3^{3k}-1 = 26k$), I want to show it for $n=k+1$ (that is, $3^{ 3(k+1)} -1=26(k+1)$). But how to proceed from here?