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A264484
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Number of (n+1) X (1+1) arrays of permutations of 0..n*2+1 with each element having directed index change 2,-1 1,0 2,1 0,-1 -2,-2 or -1,0.
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1
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1, 3, 4, 12, 25, 52, 121, 261, 576, 1280, 2809, 6204, 13689, 30167, 66564, 146804, 323761, 714136, 1575025, 3473817, 7661824, 16898560, 37271025, 82203912, 181306225, 399883707, 881971204, 1945248444, 4290381001, 9462732780
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OFFSET
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1,2
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LINKS
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FORMULA
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Empirical: a(n) = 2*a(n-1) + a(n-3) - 2*a(n-4) + 4*a(n-5) + a(n-6) - a(n-9).
Empirical g.f.: x*(1 + x - 2*x^2 + 3*x^3 - x^7) / ((1 - 2*x - x^3)*(1 + 2*x^4 - x^6)). - Colin Barker, Jan 08 2019
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EXAMPLE
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Some solutions for n=4:
..2..3....2..3....1..3....2..3....1..3....1..3....2..3....2..3....2..3....2..3
..0..1....4..5....4..5....0..5....0..5....0..5....4..1....0..1....0..1....4..1
..6..7....1..0....6..0....1..7....2..7....6..7....5..0....6..7....5..7....6..0
..8..5....8..9....8..2....8..9....8..9....8..2....8..9....8..9....8..9....8..9
..9..4....6..7....9..7....6..4....6..4....9..4....6..7....5..4....6..4....5..7
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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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