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A219498
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Number of n X 4 arrays of the minimum value of corresponding elements and their horizontal or vertical neighbors in a random, but sorted with lexicographically nondecreasing rows and nonincreasing columns, 0..1 n X 4 array.
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1
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4, 7, 18, 35, 58, 88, 126, 173, 230, 298, 378, 471, 578, 700, 838, 993, 1166, 1358, 1570, 1803, 2058, 2336, 2638, 2965, 3318, 3698, 4106, 4543, 5010, 5508, 6038, 6601, 7198, 7830, 8498, 9203, 9946, 10728, 11550, 12413, 13318, 14266, 15258, 16295, 17378
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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) = (1/6)*n^3 + 1*n^2 + (23/6)*n - 7 for n>2.
G.f.: x*(4 - 9*x + 14*x^2 - 11*x^3 + 2*x^4 + x^5) / (1 - x)^4.
a(n) = 4*a(n-1) - 6*a(n-2) + 4*a(n-3) - a(n-4) for n>6.
(End)
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EXAMPLE
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Some solutions for n=3:
..0..0..0..0....1..1..0..0....0..0..0..0....1..0..0..0....1..1..0..0
..1..0..0..0....1..1..1..0....1..0..0..0....1..0..0..0....1..1..0..0
..1..0..0..0....1..1..1..1....1..1..1..0....1..0..0..0....1..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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