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A243384
Number of length n+3 0..3 arrays with no four elements in a row with pattern abba (with a!=b) and new values 0..3 introduced in 0..3 order.
1
14, 45, 158, 579, 2165, 8173, 30991, 117755, 447850, 1704019, 6484899, 24681529, 93941906, 357565151, 1360989974, 5180318659, 19717818240, 75051888869, 285669958665, 1087345593405, 4138764004397, 15753379857391, 59962100096460
OFFSET
1,1
LINKS
FORMULA
Empirical: a(n) = 7*a(n-1) - 16*a(n-2) + 18*a(n-3) - 15*a(n-4) + 9*a(n-5) - 3*a(n-6) + a(n-7).
Empirical g.f.: x*(14 - 53*x + 67*x^2 - 59*x^3 + 40*x^4 - 13*x^5 + 5*x^6) / ((1 - x)*(1 - 2*x + x^2 - x^3)*(1 - 4*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
..1....1....1....1....0....1....1....1....0....1....1....1....0....1....1....1
..0....1....0....2....1....0....2....1....1....2....2....2....0....1....0....0
..1....1....1....3....1....1....0....2....2....1....1....3....0....1....0....0
..2....1....2....0....1....1....2....2....1....0....0....1....0....2....2....2
..1....0....3....3....0....2....1....2....1....2....1....3....0....2....2....3
CROSSREFS
Column 3 of A243389.
Sequence in context: A232872 A232855 A232791 * A242579 A206208 A328245
KEYWORD
nonn
AUTHOR
R. H. Hardin, Jun 04 2014
STATUS
approved