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A264018
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Number of (2+1) X (n+1) arrays of permutations of 0..n*3+2 with each element having index change +-(.,.) 0,0 1,2 or 2,2.
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1
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1, 5, 25, 105, 441, 1869, 7921, 33553, 142129, 602069, 2550409, 10803705, 45765225, 193864605, 821223649, 3478759201, 14736260449, 62423800997, 264431464441, 1120149658761, 4745030099481, 20100270056685, 85146110326225
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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) = 4*a(n-1) + 4*a(n-3) + a(n-4).
Empirical g.f.: x*(1 + x + 5*x^2 + x^3) / ((1 + x^2)*(1 - 4*x - x^2)). - Colin Barker, Jan 03 2019
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EXAMPLE
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Some solutions for n=4:
..7..1..2..3..4....0.13..9..3..4....0..8..9..3..4....7..1..9..3..4
.12..6..0..8..9...12..6..7..8..2...12..6.14..1..2...12.13..0..8..2
.10.11..5.13.14...10.11..5..1.14...10.11..5.13..7...10.11..5..6.14
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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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