%I #3 Mar 31 2012 12:35:46
%S 1,12,960,337680,367597440,755465356800,3208061483827200,
%T 23775433137840384000
%N Number of lexicographically ordered pairs of permutations of 0..2n-2 such that their sum mod 2n-1 is also a permutation of 0..2n-2
%C Numbers for permutations of 0..2n-1 are zero.
%K nonn
%O 1,2
%A _R. H. Hardin_ Aug 18 2010