A220628 Number of ways to reciprocally link elements of an n X n array either to themselves or to exactly two horizontal or antidiagonal neighbors.

1, 1, 3, 37, 1481, 183961, 72097810, 91163971015, 374610359478958, 4999831941923800805, 216409223358914018252290, 30357148112130816204187346595, 13800400036239294148735727438211949

Offset

1,3

Comments

Diagonal of A220632.

Links

R. H. Hardin, Table of n, a(n) for n = 1..16

Example

All solutions for n=3 0=self 3=ne 4=w 6=e 7=sw (reciprocal directions total 10)
.00.67.47...00.00.00...00.00.00
.36.34.00...00.67.47...00.00.00
.00.00.00...36.34.00...00.00.00

Crossrefs

Sequence in context: A270584 A175771 A368775 * A261594 A351759 A132931

Adjacent sequences: A220625 A220626 A220627 * A220629 A220630 A220631

Keyword

nonn

Author

R. H. Hardin, Dec 17 2012

Status

approved