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A264238
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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 1,1 0,-1 -1,1 or 0,-2.
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1
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8, 21, 89, 296, 1105, 3897, 14128, 50533, 181937, 652944, 2346977, 8429681, 30288280, 108807669, 390915337, 1404388408, 5045461169, 18126337449, 65121053504, 233954670533, 840509324641, 3019625618976, 10848352515265
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OFFSET
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1,1
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LINKS
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FORMULA
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Empirical: a(n) = 2*a(n-1) + 6*a(n-2) - a(n-3).
Empirical g.f.: x*(8 + 5*x - x^2) / (1 - 2*x - 6*x^2 + x^3). - Colin Barker, Jan 06 2019
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EXAMPLE
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Some solutions for n=4:
..2..3..4....0..1..2....0..1..2....1..2..4....2..3..4....1..3..2....2..1..4
..5..0..1....3..4..5....3..6..5....5..0..7....5..0..1....4..0..5....5..0..7
..6..7..8....6..8.10....8..9..4....6..3..8....6..8.10....8..9.10....6..3..8
.10.12.11...11.12..7...11.10..7...10.11.13...11.12..7...11..6..7....9.10.11
.13..9.14...13..9.14...12.13.14...12..9.14...13..9.14...12.13.14...12.13.14
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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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