OFFSET
2,1
EXAMPLE
The 20 planes defined by the points of the 2 X 2 X 2 grid fall into 13 families of parallel planes: 3 parallel to the faces, 4 perpendicular to the space diagonals and 6 which are the planes defined by an edge and its opposite edge. So a(2)=13.
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Clive Tooth, Mar 19 2016
STATUS
approved