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

1,2

Comments

Diagonal of A220688

Links

Table of n, a(n) for n=1..9.

Example

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

Crossrefs

Sequence in context: A220374 A220429 A210857 * A210926 A302121 A188895

Adjacent sequences: A220679 A220680 A220681 * A220683 A220684 A220685

Keyword

nonn

Author

R. H. Hardin Dec 17 2012

Status

approved