A220684 Number of ways to reciprocally link elements of an nX4 array either to themselves or to exactly two horizontal, vertical or antidiagonal neighbors

1, 37, 745, 15452, 312603, 6349886, 128995678, 2620320833, 53226950200, 1081210102382, 21962842195925, 446135673339403, 9062444632025696, 184087280486642815, 3739402357364779367, 75959240384539034764

Offset

1,2

Comments

Column 4 of A220688

Links

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

Formula

Empirical: a(n) = 15*a(n-1) +89*a(n-2) +365*a(n-3) +522*a(n-4) -1997*a(n-5) -10213*a(n-6) -23837*a(n-7) -26018*a(n-8) +7514*a(n-9) +19116*a(n-10) -3306*a(n-11) -5327*a(n-12) +2212*a(n-13) +316*a(n-14) -285*a(n-15) +12*a(n-17) -a(n-18)

Example

Some solutions for n=3 0=self 2=n 3=ne 4=w 6=e 7=sw 8=s (reciprocal directions total 10)
.00.67.48.78...68.46.46.47...00.00.00.78...00.00.68.48...68.46.46.47
.38.78.23.27...26.48.37.00...00.67.34.27...00.68.24.27...28.00.38.00
.23.26.34.00...00.23.00.00...36.46.34.00...00.26.34.00...26.46.24.00

Crossrefs

Sequence in context: A010989 A103195 A282927 * A225971 A258463 A320551

Adjacent sequences: A220681 A220682 A220683 * A220685 A220686 A220687

Keyword

nonn

Author

R. H. Hardin Dec 17 2012

Status

approved