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 A268634 Number of n X 3 0..2 arrays with some element plus some horizontally or vertically adjacent neighbor totalling two exactly once. 1
 12, 120, 840, 5178, 29772, 163878, 875592, 4578186, 23548164, 119570574, 600870336, 2993807250, 14810051580, 72819229974, 356173467576, 1734202809114, 8410141924596, 40641730213278, 195782548631472, 940481337385122 (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) = 10*a(n-1) - 29*a(n-2) + 20*a(n-3) - 4*a(n-4). Empirical g.f.: 6*x*(2 - 2*x^2 + 3*x^3) / (1 - 5*x + 2*x^2)^2. - Colin Barker, Jan 14 2019 EXAMPLE Some solutions for n=6: ..0..0..0. .1..0..0. .1..0..0. .2..1..0. .0..1..2. .1..0..1. .1..0..0 ..0..1..1. .0..1..0. .2..1..0. .1..0..0. .1..2..1. .0..1..0. .2..2..1 ..0..0..0. .1..2..1. .1..0..0. .2..1..0. .2..2..1. .1..0..0. .2..1..0 ..0..0..1. .2..2..2. .2..1..1. .2..0..0. .2..1..0. .2..1..0. .1..2..1 ..0..1..0. .2..1..2. .1..2..2. .1..0..1. .1..2..1. .0..0..0. .2..2..2 ..1..0..0. .0..0..1. .2..2..2. .2..1..0. .0..1..2. .0..0..0. .1..2..2 CROSSREFS Column 3 of A268639. Sequence in context: A056311 A009050 A067358 * A061506 A059155 A012443 Adjacent sequences:  A268631 A268632 A268633 * A268635 A268636 A268637 KEYWORD nonn AUTHOR R. H. Hardin, Feb 09 2016 STATUS approved

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Last modified July 17 02:52 EDT 2019. Contains 325092 sequences. (Running on oeis4.)