%I #3 Mar 31 2012 12:35:44
%S 1,6,90,2504,111312,7228080,645394636,75850937208,11351113909560,
%T 2107488874630336
%N Number of permutations of 2 copies of 1..n avoiding adjacent step pattern up, down, up, down, down, down
%K nonn
%O 1,2
%A _R. H. Hardin_ May 10 2010