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 A231057 Number of n X 2 0..3 arrays x(i,j) with each element horizontally or vertically next to at least one element with value (x(i,j)+1) mod 4, no adjacent elements equal, and upper left element zero. 3
 0, 2, 6, 20, 68, 230, 778, 2632, 8904, 30122, 101902, 344732, 1166220, 3945294, 13346834, 45152016, 152748176, 516743378, 1748130326, 5913882532, 20006521300, 67681576758, 228965134106, 774583500376, 2620397211992, 8864740270458 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Column 2 of A231063. LINKS R. H. Hardin, Table of n, a(n) for n = 1..210 FORMULA Empirical: a(n) = 3*a(n-1) + a(n-2) + a(n-3). Empirical g.f.: 2*x^2 / (1 - 3*x - x^2 - x^3). - Colin Barker, Feb 24 2018 EXAMPLE Some solutions for n=4: ..0..1....0..3....0..3....0..1....0..1....0..1....0..1....0..1....0..3....0..1 ..1..2....1..2....1..0....3..2....3..2....3..2....3..2....3..2....1..2....1..2 ..2..3....0..3....2..3....1..0....2..1....0..3....2..1....2..3....0..1....0..3 ..1..0....3..2....1..2....2..3....3..0....1..2....1..0....1..0....3..2....1..2 CROSSREFS Cf. A231063. Sequence in context: A027063 A291005 A027065 * A295873 A006012 A127152 Adjacent sequences: A231054 A231055 A231056 * A231058 A231059 A231060 KEYWORD nonn AUTHOR R. H. Hardin, Nov 03 2013 STATUS approved

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Last modified October 4 08:18 EDT 2023. Contains 365873 sequences. (Running on oeis4.)