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 A228797 Number of 2 X n binary arrays with top left element equal to 1 and no two ones adjacent horizontally or nw-se. 1
 2, 2, 8, 16, 42, 98, 240, 576, 1394, 3362, 8120, 19600, 47322, 114242, 275808, 665856, 1607522, 3880898, 9369320, 22619536, 54608394, 131836322, 318281040, 768398400, 1855077842, 4478554082, 10812186008, 26102926096, 63018038202, 152139002498 (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) = a(n-1) + 3*a(n-2) + a(n-3). Conjectures from Colin Barker, Sep 13 2018: (Start) G.f.: 2*x / ((1 + x)*(1 - 2*x - x^2)). a(n) = (-2*(-1)^n + (1-sqrt(2))^n + (1+sqrt(2))^n) / 2. (End) EXAMPLE Some solutions for n=4: ..1..0..0..1....1..0..0..1....1..0..0..0....1..0..0..1....1..0..0..1 ..0..0..0..0....0..0..1..0....0..0..0..1....1..0..1..0....0..0..0..1 CROSSREFS Row 2 of A228796. Sequence in context: A220172 A276054 A192305 * A052970 A220589 A109190 Adjacent sequences: A228794 A228795 A228796 * A228798 A228799 A228800 KEYWORD nonn AUTHOR R. H. Hardin, Sep 04 2013 STATUS approved

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Last modified June 2 22:56 EDT 2023. Contains 363102 sequences. (Running on oeis4.)