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A264307
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Number of (n+1) X (2+1) arrays of permutations of 0..n*3+2 with each element having directed index change 0,0 0,1 1,0 -1,-2 or 0,2.
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2
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6, 20, 68, 240, 832, 2896, 10080, 35072, 122048, 424704, 1477888, 5142784, 17895936, 62274560, 216704000, 754089984, 2624094208, 9131364352, 31775465472, 110572765184, 384772849664, 1338938621952, 4659259703296, 16213365293056
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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) = 2*a(n-1) + 4*a(n-2) + 4*a(n-3).
Empirical g.f.: 2*x*(3 + 4*x + 2*x^2) / (1 - 2*x - 4*x^2 - 4*x^3). - Colin Barker, Mar 21 2018
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EXAMPLE
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Some solutions for n=4:
..0..1..2....0..1..2....5..1..0....5..1..0....5..1..0....5..0..2....5..1..0
..8..4..3....3..4..5....8..4..2....3..4..2....3..4..2....8..1..4....8..3..2
.11..6..5....6..7..8....3..7..6...11..6..8...11..6..7....3..6..7...11..4..6
.14..7.10....9.10.11...14.10.11....9..7.10...14.10..8...14.10.11...14..7.10
..9.13.12...12.13.14....9.12.13...12.13.14....9.12.13....9.12.13....9.12.13
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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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