%I #3 Mar 31 2012 12:35:44
%S 1,6,90,2518,113052,7434180,673334112,80360724360,12221802614520,
%T 2307379944600182
%N Number of permutations of 2 copies of 1..n avoiding adjacent step pattern up, up, up, down, down, down
%K nonn
%O 1,2
%A _R. H. Hardin_ May 10 2010