%I #3 Mar 31 2012 12:35:44
%S 1,6,90,2510,112020,7307874,655845094,77496572328,11662893335890,
%T 2177988280932500
%N Number of permutations of 2 copies of 1..n avoiding adjacent step pattern up, down, down, up, up, up
%K nonn
%O 1,2
%A _R. H. Hardin_ May 10 2010