What are the i,j,k components of a 3d mesh on plot.ly (online)?

A 3d Mesh on plot.ly online graph maker (https://plot.ly/create/#/) takes 3 mandatory variables (X, Y, Z) and 3 optional variables (I, J, K). I understand that if I want to draw a cube that I then have to use the IJK-variables, since without them nothing will be drawn.

After some googling I found that with i, j, k you can represent vectors. Though I do not understand how in the following examples they correspond to the XYZ values, so that a cube can be drawn. There are several examples of cubes and cuboids on plot.ly, all of which share the same i, j, k, values. f.e. https://plot.ly/create/?fid=RPlotBot%3A3933#/

https://plot.ly/create/?fid=markope%3A143#/

Taking the first link as an example:

x   y   z       i   j   k
0   0   0       7   3   0
0   1   0       0   4   7
1   1   0       0   1   2
1   0   0       0   2   3
0   0   1       4   5   6
0   1   1       4   6   7
1   1   1       6   5   1
1   0   1       6   2   1
4   0   5
0   1   5
3   6   7
2   3   6


This will draw a normal cube. When I try my XYZ-coordinates, however, it will draw following:

My xyz-coordinates are:

x   y   z
25  25  65
25  55  65
55  25  65
55  55  65
25  25  80
25  55  80
55  25  80
55  55  80


How can I calculate the according ijk-values so that I get a cuboid? Any tips or links to resources?

The official tutorial for a 3d mesh on plot.ly online graph maker only mentions the ijk-values, doesn't explain them though.