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 A220564 Number of ways to reciprocally link elements of an 3 X n array either to themselves or to exactly one horizontal or antidiagonal neighbor. 1
 1, 13, 64, 430, 2604, 16310, 101052, 628269, 3901815, 24240377, 150578968, 935414825, 5810847665, 36097422853, 224239670624, 1392992694942, 8653368270212, 53755331997318, 333931897912068, 2074408410086741 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Row 3 of A220562. LINKS R. H. Hardin, Table of n, a(n) for n = 1..210 FORMULA Empirical: a(n) = 4*a(n-1) + 15*a(n-2) - 5*a(n-3) - 19*a(n-4) + 9*a(n-5) + 2*a(n-6) - a(n-7). Empirical g.f.: x*(1 - x)*(1 + 10*x + 7*x^2 - 9*x^3 - x^4 + x^5) / ((1 + x - x^2)*(1 - 5*x - 9*x^2 + 9*x^3 + x^4 - x^5)). - Colin Barker, Aug 01 2018 EXAMPLE Some solutions for n=3 0=self 3=ne 4=w 6=e 7=sw (reciprocal directions total 10): ..0..6..4....6..4..0....0..7..0....0..7..7....0..6..4....6..4..7....0..0..0 ..6..4..0....0..7..0....3..0..0....3..3..7....0..0..0....0..3..7....6..4..0 ..0..6..4....3..0..0....6..4..0....0..3..0....0..0..0....0..3..0....0..6..4 CROSSREFS Cf. A220562. Sequence in context: A166605 A054477 A169883 * A264513 A302161 A302633 Adjacent sequences: A220561 A220562 A220563 * A220565 A220566 A220567 KEYWORD nonn AUTHOR R. H. Hardin, Dec 16 2012 STATUS approved

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Last modified November 29 22:05 EST 2023. Contains 367452 sequences. (Running on oeis4.)