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 A269462 Number of length-n 0..3 arrays with no repeated value equal to the previous repeated value. 1
 4, 16, 60, 228, 852, 3180, 11796, 43644, 160980, 592572, 2177268, 7988700, 29277204, 107195196, 392179380, 1433907228, 5240022612, 19140884220, 69894090996, 255150047964, 931214323860, 3397977981372, 12397189043508, 45224087388060 (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) - 18*a(n-3). Conjectures from Colin Barker, Jan 22 2019: (Start) G.f.: 4*x*(1 - x - 5*x^2) / ((1 - 3*x)*(1 - 2*x - 6*x^2)). a(n) = (-28*3^n + (49-17*sqrt(7))*(1-sqrt(7))^n + (1+sqrt(7))^n*(49+17*sqrt(7))) / 63. (End) EXAMPLE Some solutions for n=9: ..1. .1. .2. .2. .0. .0. .1. .2. .1. .2. .0. .2. .1. .1. .1. .0 ..0. .1. .1. .1. .3. .2. .3. .0. .2. .1. .1. .1. .3. .2. .2. .1 ..1. .2. .2. .3. .1. .0. .2. .0. .1. .0. .3. .2. .3. .0. .2. .0 ..0. .1. .3. .0. .3. .0. .1. .2. .0. .0. .0. .1. .0. .3. .1. .1 ..1. .2. .0. .1. .1. .1. .0. .2. .3. .1. .2. .1. .3. .3. .1. .0 ..2. .3. .3. .2. .3. .2. .1. .0. .1. .3. .1. .3. .2. .1. .0. .0 ..0. .0. .0. .2. .1. .3. .2. .0. .3. .2. .1. .1. .3. .3. .3. .1 ..2. .0. .1. .0. .3. .0. .0. .2. .3. .0. .2. .0. .1. .2. .0. .1 ..2. .3. .0. .0. .2. .2. .3. .2. .2. .2. .2. .0. .0. .2. .0. .0 CROSSREFS Column 3 of A269467. Sequence in context: A072335 A081161 A032106 * A047097 A051043 A123620 Adjacent sequences:  A269459 A269460 A269461 * A269463 A269464 A269465 KEYWORD nonn AUTHOR R. H. Hardin, Feb 27 2016 STATUS approved

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Last modified January 27 09:01 EST 2020. Contains 331293 sequences. (Running on oeis4.)