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 A232956 Number of 2 X n 0..3 arrays with no element x(i,j) adjacent to value 3-x(i,j) horizontally, diagonally or antidiagonally, and top left element zero. 1
 4, 21, 129, 771, 4629, 27771, 166629, 999771, 5998629, 35991771, 215950629, 1295703771, 7774222629, 46645335771, 279872014629, 1679232087771, 10075392526629, 60452355159771, 362714130958629, 2176284785751771 (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) = 5*a(n-1) + 6*a(n-2). Conjectures from Colin Barker, Oct 06 2018: (Start) G.f.: x*(4 + x) / ((1 + x)*(1 - 6*x)). a(n) = (25*6^n - 18) / 42 for n even. a(n) = (25*6^n + 18) / 42 for n odd. (End) EXAMPLE Some solutions for n=5: ..0..1..0..2..3....0..0..0..0..1....0..0..0..1..0....0..1..1..1..0 ..3..2..0..2..2....0..1..1..0..2....0..0..1..1..0....0..0..0..1..0 CROSSREFS Row 2 of A232955. Sequence in context: A099250 A293192 A300674 * A234268 A111177 A141052 Adjacent sequences:  A232953 A232954 A232955 * A232957 A232958 A232959 KEYWORD nonn AUTHOR R. H. Hardin, Dec 02 2013 STATUS approved

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Last modified October 21 14:57 EDT 2018. Contains 316424 sequences. (Running on oeis4.)