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%I #3 Mar 31 2012 12:35:42
%S 1,6,90,2520,113400,7484400,681080400,81729648000,12504636144000,
%T 1522786801536000,152883132197796000
%N Number of permutations of 2 copies of 1..n with all adjacent differences <= 8 in absolute value.
%C a(n)=(2n)!/2^n for n<=9
%K nonn
%O 1,2
%A _R. H. Hardin_ May 06 2010
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