Search: id:A077613
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%I A077613
%S A077613 0,1,4,24,144,1080,8640,80640,806400,9072000,108864000,1437004800,
%T A077613 20118067200,305124019200,4881984307200,83691159552000,
%U A077613 1506440871936000,28810681675776000,576213633515520000
%N A077613 Number of adjacent pairs of form (even,odd) among all permutations of 
               {1,2,...,n}. Also, number of adjacent pairs of form (odd,even).
%H A077613 Leroy Quet, <a href="http://www.prism-of-spirals.net/">Home Page</a> 
               (listed in lieu of email address)
%F A077613 a(n) = floor(n/2)*ceiling(n/2)*(n-1)!. Proof: There are floor(n/2)*ceiling(n/
               2) pairs (r, s) with r even and s odd. For each pair, there are n-1 
               places it can occur in a permutation and (n-2)! possible arrangements 
               of the other numbers.
%Y A077613 Cf. A077611, A077612.
%Y A077613 Sequence in context: A067411 A045915 A052609 this_sequence A072949 A104531 
               A045738
%Y A077613 Adjacent sequences: A077610 A077611 A077612 this_sequence A077614 A077615 
               A077616
%K A077613 nonn
%O A077613 1,3
%A A077613 Leroy Quet Frank Ruskey (fruskey(AT)cs.uvic.ca) and Dean Hickerson (dean.hickerson(AT)yahoo.com), 
               Nov 11 2002

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