A220727 Number of ways to reciprocally link elements of an 3Xn array either to themselves or to exactly two horizontal, diagonal or antidiagonal neighbors

1, 4, 30, 230, 1819, 14466, 114900, 913187, 7256380, 57664692, 458236178, 3641435760, 28937067889, 229951848995, 1827338913535, 14521161884614, 115394100670410, 916992651769082, 7286988782183320, 57906904219355630

Offset

1,2

Comments

Row 3 of A220725

Links

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

Formula

Empirical: a(n) = 5*a(n-1) +24*a(n-2) -a(n-3) -25*a(n-4) -33*a(n-5) +10*a(n-6) +19*a(n-7) +4*a(n-8) -4*a(n-9) -a(n-10)

Example

Some solutions for n=3 0=self 1=nw 3=ne 4=w 6=e 7=sw 9=se (reciprocal directions total 10)
.69.49.00...00.69.47...00.67.47...69.47.00...00.79.00...00.67.47...00.69.47
.69.14.17...00.36.14...36.34.00...39.16.47...39.67.14...39.37.00...00.37.17
.00.13.00...00.00.00...00.00.00...00.13.00...36.14.00...36.14.00...36.34.00

Crossrefs

Sequence in context: A000313 A082144 A349456 * A137971 A346579 A300159

Adjacent sequences: A220724 A220725 A220726 * A220728 A220729 A220730

Keyword

nonn

Author

R. H. Hardin Dec 18 2012

Status

approved