Given an integer sequence X={x_n}_n, a natural question is to
`quantify' the number of primes dividing at least one non-zero
term of the sequence. For most naturally occurring sequences this is a
hard question, and usually we only have conjectures.
We will show that in the case of second order linear recurrent sequences,
the set of prime divisors has a natural density that, at least in principle,
can be computed exactly.