  Let D be the circulant digraph with n vertices and connection set {2,3,c}.
(Assume D is loopless and has outdegree 3.) Work of S.C.Locke and D.Witte
implies that if n is a multiple of 6, c is either (n/2) + 2 or (n/2) + 3, and c
is even, then D does not have a hamiltonian cycle. For all other cases, we
construct a hamiltonian cycle in D.
