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Search: id:A077611
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| A077611 |
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Number of adjacent pairs of form (odd,odd) among all permutations of {1,2,...,n}. |
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+0
3
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| 0, 0, 4, 12, 144, 720, 8640, 60480, 806400, 7257600, 108864000, 1197504000, 20118067200, 261534873600, 4881984307200, 73229764608000, 1506440871936000, 25609494822912000, 576213633515520000
(list; graph; listen)
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OFFSET
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1,3
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LINKS
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Leroy Quet, Home Page (listed in lieu of email address)
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FORMULA
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a(n) = ceiling(n/2)*ceiling(n/2-1)*(n-1)!. Proof: There are ceiling(n/2)*ceiling(n/2-1) pairs (r, s) with r and s odd and distinct. For each pair, there are n-1 places it can occur in a permutation and (n-2)! possible arrangements of the other numbers.
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CROSSREFS
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Cf. A077612, A077613.
Sequence in context: A009663 A002029 A152121 this_sequence A052598 A032071 A076030
Adjacent sequences: A077608 A077609 A077610 this_sequence A077612 A077613 A077614
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KEYWORD
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nonn
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AUTHOR
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Leroy Quet Frank Ruskey (fruskey(AT)cs.uvic.ca) and Dean Hickerson (dean.hickerson(AT)yahoo.com), Nov 11 2002
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