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 A221510 Number of 0..3 arrays of length n with each element differing from at least one neighbor by 2 or more, starting with 0. 1
 0, 2, 3, 12, 30, 89, 248, 706, 1995, 5652, 15998, 45297, 128240, 363074, 1027923, 2910236, 8239390, 23327177, 66043368, 186980482, 529374875, 1498754084, 4243238398, 12013359841, 34011950560, 96293859202, 272624979363 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Column 3 of A221515. LINKS R. H. Hardin, Table of n, a(n) for n = 1..210 FORMULA Empirical: a(n) = a(n-1) +4*a(n-2) +3*a(n-3) +a(n-4). Empirical g.f.: x^2*(2 + x + x^2) / ((1 + x)*(1 - 2*x - 2*x^2 - x^3)). - Colin Barker, Oct 18 2017 EXAMPLE Some solutions for n=6 ..0....0....0....0....0....0....0....0....0....0....0....0....0....0....0....0 ..2....2....2....2....2....3....2....2....3....3....2....3....3....2....3....3 ..3....0....2....1....2....0....0....3....1....3....3....2....0....1....2....3 ..0....2....0....3....0....3....1....1....0....1....1....0....3....3....0....1 ..3....2....2....0....3....0....3....1....3....3....0....3....3....3....0....0 ..0....0....0....3....1....2....1....3....0....0....2....0....1....1....2....3 CROSSREFS Sequence in context: A025560 A247651 A305746 * A109489 A169636 A105401 Adjacent sequences:  A221507 A221508 A221509 * A221511 A221512 A221513 KEYWORD nonn AUTHOR R. H. Hardin, Jan 18 2013 STATUS approved

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Last modified December 9 22:27 EST 2019. Contains 329880 sequences. (Running on oeis4.)