A220682 Number of ways to reciprocally link elements of an n X n array either to themselves or to exactly two horizontal, vertical or antidiagonal neighbors.

1, 4, 94, 15452, 15978924, 107713940118, 4701615485821782, 1328565529272722924682, 2429341045430456043662317796

Offset: 1

Author

R. H. Hardin Dec 17 2012

Keywords

• nonn

Comments

Diagonal of A220688

Examples

			Some solutions for n=3 0=self 2=n 3=ne 4=w 6=e 7=sw 8=s (reciprocal directions total 10)
.68.48.78...00.68.48...00.00.00...00.00.78...00.67.48...68.47.78...00.68.48
.28.23.28...00.26.24...00.78.00...00.36.24...38.00.27...23.37.28...68.24.28
.26.46.24...00.00.00...36.24.00...00.00.00...26.34.00...36.46.24...26.46.24