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%I #3 Mar 31 2012 12:35:44
%S 1,6,90,2436,104872,6591251,568874050,64561209403,9324840163064,
%T 1670314013465714
%N Number of permutations of 2 copies of 1..n avoiding adjacent step pattern up, down, up, up, down, up
%K nonn
%O 1,2
%A _R. H. Hardin_ May 10 2010