%I #3 Mar 31 2012 12:35:42
%S 1,6,90,2520,113400,7484400,681080400,81729648000,7580424852000,
%T 569159625434400,36636506215016400
%N Number of permutations of 2 copies of 1..n with all adjacent differences <= 7 in absolute value.
%C a(n)=(2n)!/2^n for n<=8
%K nonn
%O 1,2
%A _R. H. Hardin_ May 06 2010