  A tripartite-circle drawing of a tripartite graph is a drawing in the plane,
where each part of a vertex partition is placed on one of three disjoint
circles, and the edges do not cross the circles. The tripartite-circle crossing
number of a tripartite graph is the minimum number of edge crossings among all
its tripartite-circle drawings. We determine the exact value of the
tripartite-circle crossing number of $K_{a,b,n}$, where $a,b\leq 2$.
