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A221538
Number of 0..4 arrays of length n with each element differing from at least one neighbor by something other than 1, starting with 0.
1
0, 4, 14, 68, 303, 1386, 6311, 28762, 131012, 596784, 2718469, 12383368, 56409683, 256961576, 1170529586, 5332078812, 24289062227, 110643256974, 504010005519, 2295902089838, 10458455859448, 47641099074536, 217018109737881
OFFSET
1,2
COMMENTS
Column 4 of A221542.
LINKS
FORMULA
Empirical: a(n) = 5*a(n-1) -3*a(n-2) +a(n-3) +15*a(n-4) +3*a(n-5) for n>6.
Empirical g.f.: x^2*(4 - 6*x + 10*x^2 + x^3 + x^4) / (1 - 5*x + 3*x^2 - x^3 - 15*x^4 - 3*x^5). - 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
..4....3....4....3....2....4....4....2....3....4....3....2....4....4....4....0
..3....3....0....4....4....3....0....1....3....0....2....2....0....0....0....2
..3....1....2....4....4....0....3....1....2....1....2....0....3....1....0....4
..0....4....2....3....1....4....3....1....2....3....4....0....3....4....4....4
..3....2....2....3....3....1....3....4....2....1....0....3....1....2....2....0
CROSSREFS
Sequence in context: A292725 A292713 A007025 * A301511 A014512 A274804
KEYWORD
nonn
AUTHOR
R. H. Hardin, Jan 19 2013
STATUS
approved