%I A007868
%S A007868 1,1,2,5,17,73,398,2636,20542,182750,1819148,19976248,239570876,
%T A007868 3113794652,43590340840,653842358768,10461418047368,177843819947656
%N A007868 Number of inverse pairs of elements in symmetric group S_n, or pairs 
               of total orders on n nodes (average of A000085 and A000142).
%H A007868 T. D. Noe, <a href="b007868.txt">Table of n, a(n) for n=0..100</a>
%H A007868 P. J. Cameron, <a href="http://www.cs.uwaterloo.ca/journals/JIS/index.html">
               Sequences realized by oligomorphic permutation groups</a>, J. Integ. 
               Seqs. Vol. 3 (2000), #00.1.5.
%Y A007868 Sequence in context: A084161 A102038 A002135 this_sequence A136726 A112831 
               A000774
%Y A007868 Adjacent sequences: A007865 A007866 A007867 this_sequence A007869 A007870 
               A007871
%K A007868 nonn,nice
%O A007868 0,3
%A A007868 Peter Cameron [ P.J.Cameron(AT)qmw.ac.uk ]