  An integer sequence is called realizable if it is the count of periodic
points of some map. The Fibonacci sequence $(F_n)$ does not have this property,
and the Fibonacci sequence sampled along the squares $(F_{n^2})$ also does not
have this property. We prove that this is an arithmetic phenomenon related to
the discriminant of the Fibonacci sequence, by showing that the sequence
$(5F_{n^2})$ is realizable. More generally, we show that $(F_{n^{2k-1}})$ is
not realizable in a particularly strong sense while $(5F_{n^{2k}})$ is
realizable, for any $k\ge1$.
