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A189604
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Number of n X 3 array permutations with each element not moving, or moving one space E, S or NW.
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1
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1, 6, 20, 72, 256, 912, 3248, 11568, 41200, 146736, 522608, 1861296, 6629104, 23609904, 84087920, 299483568, 1066626544, 3798846768, 13529793392, 48187073712, 171620807920, 611236571184, 2176951329392, 7753327130544
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OFFSET
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1,2
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COMMENTS
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LINKS
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FORMULA
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Empirical: a(n) = 3*a(n-1) + 2*a(n-2).
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EXAMPLE
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Some solutions for 4 X 3:
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4 5 1 0 5 1 0 1 2 0 1 2
0 3 2 7 4 2 3 4 5 3 4 5
6 7 8 3 6 8 6 11 8 10 7 8
9 10 11 9 10 11 9 7 10 6 9 11
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4 0 1 0 1 2 4 1 2
7 3 2 3 8 5 0 3 5
10 11 5 6 4 7 6 7 8
6 9 8 9 10 11 9 10 11
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MATHEMATICA
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a[n_] := Sum[Sum[4^j Binomial[k-j+1, j], {j, 0, Quotient[k+1, 2]}]* Binomial[n-1, k], {k, 0, n-1}];
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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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