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A177290
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Number of permutations of 2 copies of 1..n with all adjacent differences <= 9 in absolute value.
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0
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1, 1, 6, 90, 2520, 113400, 7484400, 681080400, 81729648000, 12504636144000, 2375880867360000, 367786358267328000, 47683626117839712000
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OFFSET
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0,3
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LINKS
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FORMULA
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a(n) = (2n)!/2^n for n<=10.
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CROSSREFS
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KEYWORD
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nonn,more
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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