  We consider primitive divisors of terms of integer sequences defined by
quadratic polynomials. Apart from some small counterexamples, when a term has a
primitive divisor, that primitive divisor is unique. It seems likely that the
number of terms with a primitive divisor has a natural density. We discuss two
heuristic arguments to suggest a value for that density, one using recent
advances made about the distribution of roots of polynomial congruences.
