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 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
 1, 8, 21, 95, 324, 1277, 4673, 17768, 66245, 249499, 934816, 3511945, 13175625, 49465544, 185641901, 696836263, 2615432756, 9816980965, 36846924297, 138302568456, 519106314333, 1948425878179, 7313254531824, 27449718110385 (list; graph; refs; listen; history; text; internal format)
 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

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Last modified September 16 04:06 EDT 2024. Contains 375959 sequences. (Running on oeis4.)