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Number of permutations of 2 copies of 1..n with all adjacent differences <= 8 in absolute value.
0

%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