A177559 - OEIS

%I #6 Nov 02 2013 18:38:14

%S 1,6,90,2448,105218,6572088,562874958,63344668632,9067009872984,

%T 1608913338743280,346665863545391736,89160540714537206616,

%U 26982910637581823115028,9492077262717161359915632

%N Number of permutations of 2 copies of 1..n avoiding adjacent step pattern up, down, down, down.

%K nonn

%O 1,2

%A _R. H. Hardin_, May 10 2010

%E a(11)-a(14) from _Alois P. Heinz_, Nov 02 2013