%I #3 Mar 31 2012 12:35:44
%S 1,6,90,2496,110760,7183476,640668497,75212295268,11244165636152,
%T 2085704995841392
%N Number of permutations of 2 copies of 1..n avoiding adjacent step pattern up, up, down, down, up, up
%K nonn
%O 1,2
%A _R. H. Hardin_ May 10 2010