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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
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
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
KEYWORD
nonn
AUTHOR
R. H. Hardin Dec 17 2012
STATUS
approved