A220721 Number of ways to reciprocally link elements of an nX4 array either to themselves or to exactly two horizontal, diagonal or antidiagonal neighbors

1, 21, 230, 2586, 29310, 331589, 3751888, 42452438, 480346122, 5435081884, 61497557384, 695840407309, 7873383816355, 89086767652576, 1008010323915227, 11405563810447637, 129053128472692922, 1460226802057078840

Offset

1,2

Comments

Column 4 of A220725

Links

R. H. Hardin, Table of n, a(n) for n = 1..210

Formula

Empirical: a(n) = 9*a(n-1) +20*a(n-2) +64*a(n-3) +65*a(n-4) +51*a(n-5) -90*a(n-6) -76*a(n-7) -34*a(n-8) +21*a(n-9) +13*a(n-10) -a(n-11) -a(n-12)

Example

Some solutions for n=3 0=self 1=nw 3=ne 4=w 6=e 7=sw 9=se (reciprocal directions total 10)
.69.47.00.00...00.79.69.47...00.79.79.00...00.00.00.00...00.00.69.47
.36.14.79.00...36.49.13.17...36.34.19.17...00.69.49.00...69.49.37.17
.00.36.46.14...00.00.13.00...00.00.36.14...00.00.16.14...00.13.13.00

Crossrefs

Sequence in context: A161518 A162360 A161899 * A320588 A020267 A188354

Adjacent sequences: A220718 A220719 A220720 * A220722 A220723 A220724

Keyword

nonn

Author

R. H. Hardin Dec 18 2012

Status

approved