Sorted edges (pairs of vertices) on a tetrahedron.
1, 2, 1, 3, 1, 4, 2, 1, 2, 3, 2, 4, 3, 1, 3, 2, 3, 4, 4, 1, 4, 2, 4, 3
1
The vertices are labeled 1 to 4. Each edge appears twice: (a,b) and (b,a).
T. D. Noe, Plot of 12 pairs
T. D. Noe, Points on a tetrahedron
Eric W. Weisstein, MathWorld: Tetrahedron
nonn,full
T. D. Noe, Jan 29 2016