%I #3 Mar 31 2012 12:35:44
%S 1,6,90,2510,111924,7292080,653417953,77078901216,11579203589017,
%T 2158323961477372
%N Number of permutations of 2 copies of 1..n avoiding adjacent step pattern up, down, down, down, up, up
%K nonn
%O 1,2
%A _R. H. Hardin_ May 10 2010