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A177284
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Number of permutations of 2 copies of 1..n with all adjacent differences <= 3 in absolute value.
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1
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1, 1, 6, 90, 2520, 41580, 516180, 6068622, 76331906, 958679970, 11679900408, 138047313960, 1610654864328, 18649754961744, 214256589488616, 2439692058769566, 27562317214408488, 309367132582535226, 3453299423388485028, 38354816922190327314, 424048220090513056908
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OFFSET
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0,3
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COMMENTS
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a(n) = (2n)!/2^n for n<=4.
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LINKS
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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