OFFSET
1,3
LINKS
Omar Sehlouli, Marko Riedel, Hexagon coloring
FORMULA
For n>=2, (1/4)(n-1)! + (1/4)n! + (1/(4n)) * Sum_{p=0..n} C(n,p) ((-1)^p/2^(n-p)) ((2n-p)! + p(2n-p-1)!).
EXAMPLE
When n=2 the coloring of the nodes of the square with two instances each of black and white must alternate and a rotation by Pi/4 takes one coloring to the other, so there is just one coloring.
CROSSREFS
KEYWORD
nonn
AUTHOR
Marko Riedel, Apr 01 2017
STATUS
approved