9, 19, 36, 62, 102, 153, 229, 324, 447, 603, 798, 1029, 1318, 1657, 2055, 2528, 3077, 3699, 4430, 5250, 6180, ... .

Geometry and topology

A complete graph with nodes is the edge graph of an -dimensional simplex. Geometrically forms the edge set of a triangle, a tetrahedron, etc. The Császár polyhedron, a nonconvex polyhedron