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 A206687 Number of n X 2 0..3 arrays with no element equal to another within two positions in the same row or column, and new values 0..3 introduced in row major order. 3
 1, 4, 11, 36, 116, 376, 1216, 3936, 12736, 41216, 133376, 431616, 1396736, 4519936, 14626816, 47333376, 153174016, 495681536, 1604059136, 5190844416, 16797925376, 54359228416, 175910158336, 569257230336, 1842155094016, 5961339109376 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Column 2 of A206692. LINKS R. H. Hardin, Table of n, a(n) for n = 1..210 FORMULA Empirical: a(n) = 2*a(n-1) + 4*a(n-2) for n>4. Conjectures from Colin Barker, Feb 23 2018: (Start) G.f.: x*(1 - x)*(1 + x)*(1 + 2*x) / (1 - 2*x - 4*x^2). a(n) = ((1-sqrt(5))^n*(-5+3*sqrt(5)) + (1+sqrt(5))^n*(5+3*sqrt(5))) / (16*sqrt(5)) for n>2. (End) EXAMPLE All solutions for n=4: ..0..1....0..1....0..1....0..1....0..1....0..1....0..1....0..1....0..1 ..2..3....1..0....2..3....1..0....2..3....1..2....1..2....1..2....1..0 ..1..2....2..3....1..0....2..3....3..2....2..0....3..0....2..3....2..3 ..0..1....3..2....3..1....3..1....1..0....3..1....0..1....0..1....0..1 CROSSREFS Cf. A206692. Sequence in context: A114248 A149237 A054577 * A106640 A109268 A256960 Adjacent sequences:  A206684 A206685 A206686 * A206688 A206689 A206690 KEYWORD nonn AUTHOR R. H. Hardin, Feb 11 2012 STATUS approved

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Last modified September 18 13:34 EDT 2020. Contains 337169 sequences. (Running on oeis4.)