  Whitney proved in 1931 that every 4-connected planar triangulation is
hamiltonian. Later in 1979, Hakimi, Schmeichel and Thomassen conjectured that
every such triangulation on $n$ vertices has at least $2(n - 2)(n - 4)$
hamiltonian cycles. Along this direction, Brinkmann, Souffriau and Van Cleemput
established a linear lower bound on the number of hamiltonian cycles in
4-connected planar triangulations. In stark contrast, Alahmadi, Aldred and
Thomassen showed that every 5-connected triangulation of the plane or the
projective plane has exponentially many hamiltonian cycles. This gives the
motivation to study the number of hamiltonian cycles of 4-connected
triangulations with few 4-separators. Recently, Liu and Yu showed that every
4-connected planar triangulation with $O(n / \log n)$ 4-separators has a
quadratic number of hamiltonian cycles. By adapting the framework of Alahmadi
et al. we strengthen the last two aforementioned results. We prove that every
4-connected planar or projective planar triangulation with $O(n)$ 4-separators
has exponentially many hamiltonian cycles.
