  We study the primitive divisors of the terms of $(\Delta_n)_{n \geq 1}$,
where $\Delta_n=N_{K/ \mathbb{Q}}(u^n-1)$ for $K$ a real quadratic field, and
$u>1$ a unit element of its ring of integers. The methods used allow us to find
the terms of the sequence that do not have a primitive prime divisor.
