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A203365
Number of n X 2 0..2 arrays with every 1 immediately preceded by 0 to the left or above, and every 2 immediately preceded by both a 1 and a 0.
1
2, 9, 30, 110, 390, 1399, 4998, 17881, 63940, 228680, 817820, 2924801, 10460002, 37408329, 133784090, 478454630, 1711106370, 6119462399, 21885149998, 78268279361, 279912339880, 1001055838960, 3580095086040, 12803562326001
OFFSET
1,1
COMMENTS
Column 2 of A203371.
LINKS
FORMULA
Empirical: a(n) = 2*a(n-1) +5*a(n-2) +2*a(n-3) +a(n-4).
Empirical g.f.: x*(2 + 5*x + 2*x^2 + x^3) / (1 - 2*x - 5*x^2 - 2*x^3 - x^4). - Colin Barker, Jun 04 2018
EXAMPLE
Some solutions for n=4:
..0..1....0..0....0..0....0..0....0..1....0..0....0..1....0..1....0..0....0..0
..1..0....0..0....0..0....0..0....0..2....0..0....0..1....0..1....0..0....1..1
..0..0....1..0....1..2....0..0....1..0....0..0....0..0....0..2....0..1....0..0
..1..2....0..0....0..0....0..1....0..1....0..0....0..1....0..0....0..0....0..1
CROSSREFS
Cf. A203371.
Sequence in context: A261330 A101604 A234007 * A181954 A343565 A318101
KEYWORD
nonn
AUTHOR
R. H. Hardin, Dec 31 2011
STATUS
approved