%I #3 Mar 31 2012 12:35:44
%S 1,6,90,2520,113256,7457040,676387059,80853167472,12317360601240,
%T 2329487321538500
%N Number of permutations of 2 copies of 1..n avoiding adjacent step pattern up, up, down, down, down, down
%K nonn
%O 1,2
%A _R. H. Hardin_ May 10 2010
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