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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 0
1, 4, 94, 15452, 15978924, 107713940118, 4701615485821782, 1328565529272722924682, 2429341045430456043662317796 (list; graph; refs; listen; history; text; internal format)
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

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Last modified January 19 14:34 EST 2022. Contains 350466 sequences. (Running on oeis4.)