%I #6 Jan 18 2016 18:29:15
%S 1,1,20,1680,51240,1173512,31006978,788946320,18721725280,
%T 435630242080,9998202729808,225310437716462
%N Number of permutations of 3 copies of 1..n with all adjacent differences <= 2 in absolute value.
%C a(n) = (3n)!/6^n for n<=3.
%Y Cf. A014606.
%K nonn
%O 0,3
%A _R. H. Hardin_, May 06 2010
%E a(0) and a(11) from _Alois P. Heinz_, Jan 18 2016