A220611 Number of ways to reciprocally link elements of an n X 5 array either to themselves or to exactly two horizontal and vertical neighbors, without consecutive collinear links.

1, 8, 21, 95, 324, 1277, 4673, 17768, 66245, 249499, 934816, 3511945, 13175625, 49465544, 185641901, 696836263, 2615432756, 9816980965, 36846924297, 138302568456, 519106314333, 1948425878179, 7313254531824, 27449718110385

Offset

1,2

Comments

Column 5 of A220614.

Links

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

Formula

Empirical: a(n) = 3*a(n-1) + 6*a(n-2) - 11*a(n-3) - 5*a(n-4) + 6*a(n-5).

Empirical g.f.: x*(1 + 5*x - 9*x^2 - 5*x^3 + 6*x^4) / (1 - 3*x - 6*x^2 + 11*x^3 + 5*x^4 - 6*x^5). - Colin Barker, Aug 01 2018

Example

Some solutions for n=3 0=self 2=n 4=w 6=e 8=s (reciprocal directions total 10):
.00.00.00.00.00...00.00.68.48.00...68.48.00.00.00...00.00.00.00.00
.68.48.00.68.48...68.48.26.24.00...26.24.68.48.00...00.00.00.68.48
.26.24.00.26.24...26.24.00.00.00...00.00.26.24.00...00.00.00.26.24

Crossrefs

Cf. A220614.

Sequence in context: A264238 A188700 A054855 * A297340 A220580 A100903

Adjacent sequences: A220608 A220609 A220610 * A220612 A220613 A220614

Keyword

nonn

Author

R. H. Hardin, Dec 17 2012

Status

approved