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A202730
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Number of n X 3 nonnegative integer arrays each row and column an ascent sequence (interior element no greater than one plus up-steps preceding it) and the lower right element equal to min(n,3)-1.
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1
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1, 2, 2, 14, 78, 406, 2062, 10374, 51998, 260246, 1301742, 6509734, 32550718, 162757686, 813796622, 4068999494, 20345030238, 101725216726, 508626214702, 2543131335654, 12715657202558, 63578287061366, 317891437403982
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OFFSET
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1,2
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COMMENTS
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LINKS
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FORMULA
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Empirical: a(n) = 7*a(n-1) -10*a(n-2) for n>4.
G.f.: x*(1 - 5*x - 2*x^2 + 20*x^3) / ((1 - 2*x)*(1 - 5*x)).
a(n) = (4*5^n - 25*2^n)/150 for n>2.
(End)
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EXAMPLE
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Some solutions for n=4:
..0..0..0....0..0..0....0..0..0....0..0..0....0..0..0....0..0..0....0..0..0
..0..0..1....0..1..1....0..1..1....0..0..0....0..0..1....0..1..0....0..0..1
..0..1..2....0..1..2....0..1..0....0..0..1....0..1..0....0..1..1....0..0..0
..0..1..2....0..1..2....0..1..2....0..1..2....0..1..2....0..1..2....0..1..2
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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