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A173847
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Number of permutations of 1..n with no adjacent pair summing to n+7.
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0
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1, 1, 2, 6, 24, 120, 720, 5040, 30240, 282240, 2338560, 26853120, 280143360, 3802982400, 47638886400, 745007155200, 10872058982400, 192275074252800, 3200021920972800, 63107717389516800, 1178953777845043200, 25641537378199142400, 531103116540719923200
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OFFSET
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0,3
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COMMENTS
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If a(n,k) is the number of permutations of 1..n with no adjacent pair summing to n+k, then a(n,k) = a(n,k+1) for n+k even.
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LINKS
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FORMULA
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k = 7; m = max(0,floor((n-k+1)/2)); a(n,k) = Sum_{j=0..m} (-2)^j C(m,j) (n-j)!.
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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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