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A243383
Number of length n+3 0..2 arrays with no four elements in a row with pattern abba (with a!=b) and new values 0..2 introduced in 0..2 order.
1
13, 35, 96, 265, 733, 2029, 5618, 15557, 43081, 119303, 330384, 914929, 2533705, 7016569, 19430930, 53809925, 149015413, 412667243, 1142796240, 3164736889, 8764081669, 24270304357, 67211568290, 186128482181, 515444182609
OFFSET
1,1
LINKS
FORMULA
Empirical: a(n) = 4*a(n-1) - 4*a(n-2) + 2*a(n-3) - a(n-4).
Empirical g.f.: x*(13 - 17*x + 8*x^2 - 5*x^3) / ((1 - x)*(1 - 3*x + x^2 - x^3)). - Colin Barker, Nov 02 2018
EXAMPLE
Some solutions for n=3:
..0....0....0....0....0....0....0....0....0....0....0....0....0....0....0....0
..0....0....0....1....0....1....1....1....0....1....1....1....0....0....0....0
..0....1....1....0....1....2....0....1....0....0....0....2....1....1....1....1
..1....2....1....2....0....0....2....1....1....2....2....2....2....2....0....2
..0....2....2....0....1....2....1....1....2....1....1....2....1....0....2....1
..1....2....2....0....0....0....0....2....0....1....2....0....0....0....2....1
CROSSREFS
Column 2 of A243389.
Sequence in context: A368361 A227986 A228024 * A242578 A192145 A221592
KEYWORD
nonn
AUTHOR
R. H. Hardin, Jun 04 2014
STATUS
approved