OFFSET
1,1
COMMENTS
Also 0..2 arrays with no 2 X 2 subblock having equal diagonal elements or equal antidiagonal elements.
LINKS
R. H. Hardin, Table of n, a(n) for n = 1..210
FORMULA
Empirical: a(n) = 15*a(n-1) - 270*a(n-3) + 324*a(n-4).
Empirical g.f.: 576*x*(4 - 6*x - 81*x^2 + 108*x^3) / ((1 - 15*x + 18*x^2)*(1 - 18*x^2)). - Colin Barker, Mar 03 2018
EXAMPLE
Some solutions for n=5:
0 2 0 1 2 2 2 1 2 0 2 2 0 0 2 2 0 0 0 2
0 1 0 1 0 1 0 1 2 0 1 1 1 1 2 2 1 1 1 1
2 1 2 2 0 1 2 1 2 0 2 2 0 0 0 2 0 2 2 2
2 0 0 1 1 1 2 1 2 1 1 1 1 1 2 2 0 1 0 1
1 1 2 2 0 1 0 0 2 1 2 2 2 0 2 1 0 1 2 1
0 0 0 1 0 2 2 1 2 1 0 0 1 0 1 1 2 1 2 0
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Jan 10 2012
STATUS
approved