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A220033
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Number of 3 X n arrays of the minimum value of corresponding elements and their horizontal or diagonal neighbors in a random, but sorted with lexicographically nondecreasing rows and nonincreasing columns, 0..1 3 X n array.
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1
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4, 6, 10, 19, 30, 42, 55, 69, 84, 100, 117, 135, 154, 174, 195, 217, 240, 264, 289, 315, 342, 370, 399, 429, 460, 492, 525, 559, 594, 630, 667, 705, 744, 784, 825, 867, 910, 954, 999, 1045, 1092, 1140, 1189, 1239, 1290, 1342, 1395, 1449, 1504, 1560, 1617, 1675
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OFFSET
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1,1
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COMMENTS
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LINKS
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FORMULA
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Empirical: a(n) = (1/2)*n^2 + (13/2)*n - 15 for n>3.
G.f.: x*(4 - 6*x + 4*x^2 + 3*x^3 - 3*x^4 - x^5) / (1 - x)^3.
a(n) = 3*a(n-1) - 3*a(n-2) + a(n-3) for n>6.
(End)
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EXAMPLE
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Some solutions for n=3:
..1..0..0....0..0..0....1..0..0....0..0..0....1..0..0....0..0..0....0..0..0
..1..1..1....1..1..0....1..0..0....1..0..0....1..0..0....0..0..0....0..0..0
..1..1..1....1..1..1....1..1..1....1..0..0....1..0..0....0..0..0....1..1..0
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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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