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 A268972 Number of 2 X n 0..2 arrays with some element plus some horizontally or antidiagonally adjacent neighbor totalling two not more than once. 1
 9, 60, 240, 912, 3312, 11664, 40176, 136080, 454896, 1504656, 4933872, 16061328, 51963120, 167226768, 535692528, 1709114256, 5433452784, 17218688400, 54411055344, 171498136464, 539289320688, 1692252695952, 5299912289520 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS R. H. Hardin, Table of n, a(n) for n = 1..210 FORMULA Empirical: a(n) = 6*a(n-1) - 9*a(n-2) for n>4. Conjectures from Colin Barker, Jan 17 2019: (Start) G.f.: 3*x*(3 - x)*(1 + x - 4*x^2) / (1 - 3*x)^2. a(n) = 16*3^(n-3) * (4*n+3) for n>2. (End) EXAMPLE Some solutions for n=4: ..0..1..0..1. .2..2..1..2. .1..2..1..0. .2..1..0..0. .1..1..2..2 ..0..0..0..2. .2..2..2..2. .2..2..1..0. .2..1..2..2. .2..2..2..1 CROSSREFS Row 2 of A268971. Sequence in context: A099333 A098327 A118674 * A288962 A074431 A268965 Adjacent sequences:  A268969 A268970 A268971 * A268973 A268974 A268975 KEYWORD nonn AUTHOR R. H. Hardin, Feb 16 2016 STATUS approved

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Last modified December 13 08:08 EST 2019. Contains 329968 sequences. (Running on oeis4.)